Arch Chemicals Provides Update on Contract to Supply Hydrazine Propellants to the U.S. Government.

NORWALK, Conn. -- Arch Chemicals, Inc. (NYSE:ARJ) has been notified that the U.S. Defense Energy Support Center (DESC) has denied the protest filed by a competing bidder of the DESC's March 29, 2005 award of a contract to the Company for the production, storage, distribution and handling of hydrazine propellants. Consequently, the suspension of the contract has been lifted, and Arch Chemicals has been instructed to re-initiate contract performance.

As stated in the Company's April 14, 2005 press release, full-scale production under this new, long-term contract was not scheduled to begin until 2007. Since there are no revenues and only minimal incremental costs associated with the awarding of this contract in the current year, the Company does not expect this action to have a significant impact on Arch's financial performance in 2005.

It remains possible that the unsuccessful bidders may still pursue additional protests or appeals regarding the award of the contract to the Company.

Headquartered in Norwalk, Connecticut, Arch Chemicals, Inc. is a global specialty chemicals company with more than $1 billion in annual sales. Arch and its subsidiaries have leadership positions in the Treatment and Performance Products segments, where they serve leading customers with forward-looking solutions to meet their chemical needs. Together with its subsidiaries, Arch has approximately 2,700 employees and manufacturing and customer-support facilities in North and South America, Europe, Asia and Africa.

Except for historical information contained herein, the information set forth in this communication may contain forward-looking statements that are based on management's beliefs, certain assumptions made by management and management's current expectations, outlook, estimates and projections about the markets and economy in which the Company and its various businesses operate. Words such as "anticipates," "believes," "estimates," "expects," "forecasts," "opines," "plans," "predicts," "projects," "should," "targets" and variations of such words and similar expressions are intended to identify such forward-looking statements. These statements are not guarantees of future performance and involve certain risks, uncertainties and assumptions ("Future Factors"), which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expected or forecasted in such forward-looking statements. The Company undertakes no obligation to update publicly any forward-looking statements, whether as a result of future events, new information or otherwise. Future Factors which could cause actual results to differ materially from those discussed include but are not limited to: general economic and business and market conditions; lack of moderate growth or recession in U.S. and European economies; increases in interest rates; economic conditions in Asia; worsening economic and political conditions in Venezuela; changes in foreign currencies against the U.S. dollar; customer acceptance of new products; efficacy of new technology; changes in U.S. laws and regulations; increased competitive and/or customer pressure; the Company's ability to maintain chemical price increases; higher-than-expected raw material costs for certain chemical product lines; an increase in anti-dumping duties on certain products; increased foreign competition in the calcium hypochlorite markets; unfavorable court, arbitration or jury decisions or tax matters; the supply/demand balance for the Company's products, including the impact of excess industry capacity; failure to achieve targeted cost-reduction programs; capital expenditures in excess of those scheduled; environmental costs in excess of those projected; the occurrence of unexpected manufacturing interruptions/outages at customer or company plants; reduction in expected government contract orders and/or the overturning of the award to the Company of the new U.S. government contract for hydrazine propellants; unfavorable weather conditions for swimming pool use; inability to expand sales in the professional pool dealer market; and gains or losses on derivative instruments.