USinternetworking Announces Client Wins; Clients Select Leading ASP to Provide Mission-Critical Business Solutions.

Business/Technology Editors

ANNAPOLIS, Md.--(BUSINESS WIRE)--Dec. 13, 2000

USinternetworking, Inc. (USi, Nasdaq: USIX), the leading Application Service Provider, today announced that several new clients have contracted to receive USi's Internet Managed Application Provider (iMAP) solutions. All iMAP clients will receive the functionality of best-of-breed software solutions as an integrated, continuously supported, flat-rate monthly service via USi's advanced global network, the USi Global Services Platform (USiGSP).

USi is pleased to announce the following companies as iMAP clients:

- Digital System Resources will be using USi's Enterprise Messaging &
Collaboration powered by Microsoft Exchange Server.

- Pantellos will be using USi's Siebel eBusiness Applications and USi's
Financial Management powered by PeopleSoft.

- Senco Products, Inc. will be using USi's Human Resource Solution powered by
PeopleSoft.

These companies chose full service provider USi out of a need to continue growing their businesses quickly and efficiently, while incurring little upfront cost. USi delivers scalable, mission-critical business solutions via best-of-breed software offerings on a standalone or in an integrated capacity. All USi clients benefit from USi's architecture including comprehensive network infrastructure and monitoring, failover services and data centers. In addition to receiving an industry-leading Service Level Agreement (SLA), USi's clients also receive best-practices implementation, consulting, hosting, management and 24x7 client services support. As part of an on-going mission to make software simple, USi takes total responsibility for the delivery of mission-critical business solutions.

About Digital System Resources

DSR provides solutions for complex processing systems for the federal government and commercial industries. In the Federal marketplace, DSR is a recognized leader in providing state of the art high quality products for the development and production of systems for passive and active sonar, electronic warfare, combat control, and computer based training and simulation for these systems. In the commercial sector, our eCommerce System group is focusing on the fastest growing portion of eCommerce, the business to business (B2B) sector. DSR services and products not only utilize today's technology but are designed to allow for the rapid introduction of tomorrow's technology.Visit the DSR website at www.dsrnet.com

About Pantellos

Pantellos is an online Marketplace providing supply chain solutions and services to the utility and energy industries. The company focuses on tackling supply chain challenges, and managing a dynamic marketplace that creates value for buyers, suppliers and other supply chain participants. Pantellos is developing solutions in an open environment that enables all members to conduct supply chain activities and transactions through its secure, Internet-based Marketplace. The 21 founding members of Pantellos are some of the largest utility and energy companies in North America. They include American Electric Power, Carolina Power & Light, CINERGY, Consolidated Edison, Dominion Resources, DTE Energy, Duke Energy, Edison International, El Paso Energy, Entergy, FirstEnergy Corp., FPL Group, GPU, Ontario Power Generation, PG&E Corporation, Public Services Enterprise Group, Reliant Energy, Sempra Energy, Southern Company, TXU and Exelon. Visit the Pantellos website at www.pantellos.com.

About Senco Products, Inc.

Cincinnati-based Senco Products Inc. was founded in 1951. Today, SENCO is one of the world's leading manufacturers of power fastening systems. Our worldwide network of manufacturing facilities, home improvement center channels, authorized dealers, distributors and sales representatives offer customers in North and South America, Europe, Asia and Australia a convenient source for our tools, fasteners, accessories, systems and service.

About USinternetworking, Inc.

USinternetworking Inc. (Nasdaq: USIX), a leading Application Service Provider delivering e-commerce and enterprise software as a service. The company's iMAP portfolio of service offerings delivers the functionality of leading software from Ariba, BroadVision, Lawson, Microsoft, Oracle, PeopleSoft and Siebel as a continuously supported, flat-rate monthly service via an advanced, secure global data center network. Additionally, USi's AppHost managed application hosting services provide the most advanced solutions for enterprises, software companies, marketplaces, and system integrators who are looking for a better way to deliver solutions over the Internet to their customers and end users. For more information, visit www.usi.com.

Internet Managed Application Provider, iMAP, AppHost, PriorityPeering, USiGSP, USiSAN UsiAccelerate,and Making Software Simple are service marks of USinternetworking, Inc. All other trademarks are the property of their respective owners. USi strategic partners and providers are publicly traded on Nasdaq under the symbols: ARBA, BVSN, CSCO, MSFT, ORCL, PSFT and SEBL.

Information in this release may involve expectations, beliefs, plans, intentions or strategies regarding the future. These forward-looking statements involve risks and uncertainties. All forward-looking statements included in this release are based upon information available to USinternetworking Inc. as of the date of the release, and we assume no obligation to update any such forward-looking statement. The statements in this release are not guarantees of future performance and actual results could differ materially from our current expectations. Numerous factors could cause or contribute to such differences. Some of the factors and risks associated with our business are discussed in the Company's registration statement on Form S-3 declared effective by the Securities and Exchange Commission ("SEC") on October 24, 2000, the Company's Form 10-Q filed with the SEC on November 14, 2000, and in our other reports filed from time to time with the SEC.