EXHIBIT 99.1

  NEWS RELEASE
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                                                                   [ARCH LOGO]
  Arch Chemicals, Inc.
  501 Merritt 7
  P.O. Box 5204
  Norwalk, CT 06856



                               Investor Contact: MARK E. FAFORD (203) 229-2654

                                  Press Contact: DALE N. WALTER (203) 229-3033



                 ARCH CHEMICALS COMPLETES BIOCIDES ACQUISITION



NORWALK, CT, April 5, 2004 -- Arch Chemicals, Inc. (NYSE: ARJ) reported today
that it has completed its previously announced acquisition of the Biocides
business of Avecia, which is comprised of a Pool & Spa business and a
Protection & Hygiene business. The two businesses had combined sales of
approximately $137 million in 2003.

"We are very pleased to add these businesses to our Treatment Products
segment. They will greatly complement Arch's existing capabilities in water
treatment and industrial biocides and present us with many exciting
synergies," said Arch Chemicals' Chairman, President and CEO Michael E.
Campbell. "The acquisition of the Pool & Spa business will rapidly accelerate
our participation in the specialty pool and spa dealer channel while the
Protection & Hygiene business provides opportunities for Arch to expand our
product offerings in the industrial and consumer segments of the biocides
market," Mr. Campbell added.

Included in the acquisition are manufacturing centers located in the United
Kingdom, with additional toll manufacturing and customer support capabilities
worldwide.

The total purchase price is approximately $215 million, consisting of $200
million in cash and 669,750 shares of Arch common stock. The purchase price is
subject to a post-closing working






capital adjustment and a $5 million contingent payment based upon future
performance of the acquired businesses. The acquisition is expected to be cash
and earnings accretive in 2004, excluding synergies.

Mr. Campbell concluded, "Our transition teams are already efficiently
integrating the two organizations, and we expect to rapidly capitalize on the
many growth opportunities and cost synergies we have identified. These
acquired businesses are staffed with very talented and innovative individuals,
and we welcome them to the Arch family."

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Headquartered in Norwalk, Connecticut, Arch Chemicals, Inc. is a global
specialty chemicals company with $1 billion in annual sales. Together with its
subsidiaries, Arch has 3,000 employees and manufacturing and customer support
centers in North America, South America, Europe, Asia and Africa. Arch and its
subsidiaries have leadership positions in three business segments -- Treatment
Products, Microelectronic Materials and Performance Products -- and they serve
leading customers in these markets with forward-looking solutions to their
chemical needs. For more information, visit www.archchemicals.com.

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Except for historical information contained herein, the information set forth
in this communication contains forward-looking statements that are based on
management's beliefs, certain assumptions made by management and management's
current expectations, estimates and projections about the markets and economy
in which Arch and its various businesses operate. Words such as "anticipates,"
"believes," "estimates," "expects," "forecasts," "opines," "plans,"
"predicts," "projects," "should," "targets," "will," 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 economic recovery






in 2004 in the U.S.; lack of moderate growth or recession in European
economies; increases in interest rates; economic conditions in Asia; worsening
economic and political conditions in Venezuela; strengthening of the U.S.
dollar against foreign currencies; 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; increased foreign competition in the calcium
hypochlorite markets; lack of continued recovery in the semiconductor
industry; unfavorable court, arbitration or jury decisions; the supply/demand
balance for the Company's products, including the impact of excess industry
capacity; failure to achieve targeted cost-reduction programs; unsuccessful
entry into new markets for electronic chemicals; 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
failure to renew or extend the 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.