SAN DIEGO, California—April 2, 2001—MDL Information Systems, Inc., the recognized leader in discovery informatics for the life sciences and chemistry in industry and academia, and Sigma-Aldrich, a leading Life Science and High Technology company, have signed an agreement to provide customers more timely and accurate access to chemical sourcing and procurement information. MDL and Sigma-Aldrich announced the agreement at the 221st National Meeting and Exposition of the American Chemical Society (ACS), April 2-4, at the San Diego Convention Center, San Diego, California.

Under the agreement, Sigma-Aldrich will provide its catalog data directly to MDL for inclusion in MDL's Available Chemicals Directory (ACD), a structure-searchable chemicals database with pricing and supplier information for over a quarter of a million research-grade and bulk chemicals. With this addition, chemists and researchers using ACD will be assured of the timeliness and quality of the Sigma-Aldrich content in ACD. MDL will provide Sigma-Aldrich with MDL numbers (which uniquely identify chemical structures) for the compounds in the Sigma-Aldrich brand catalogs, as well as those compounds available through the Sigma-Aldrich Library of Rare Chemicals. Sigma-Aldrich will add the MDL numbers as part of its extensive, searchable product content available on their award winning Web site. This exchange will allow ACD users and Sigma-Aldrich customers the ease and convenience of purchasing supplies from Sigma-Aldrich using an MDL number.

"This agreement is great news for our mutual customers," said Phil McHale, D.Phil., vice president of marketing for MDL. "Sigma Aldrich is leading the way in helping implement MDL's strategy to reach out to all ACD partners to ensure up-to-date and accurate catalog information for the thousands of researchers who use ACD everyday to locate reagents and starting compounds."

The agreement between MDL and Sigma-Aldrich contemplates collaboration in the development of more direct links between MDL's sourcing and chemical management applications (such as Reagent Selector, CIMS and SMART) and Sigma-Aldrich's e-Commerce-enabled Internet applications, opening the door to seamless online chemical sourcing, ordering, and tracking.

"This cooperative venture between the two key players in chemical sourcing will provide immediate benefits to researchers, including streamlining the process of purchasing those materials through Sigma-Aldrich," said John Radke, Manager-Laboratory Essentials for Sigma-Aldrich. "But equally exciting are the possibilities this presents for future collaboration and simplified chemical sourcing solutions for our mutual customers."

MDL Information Systems ("MDL") is the recognized leader in discovery informatics for the life sciences and chemistry in industry and academia. MDL software, content, and services provide the enterprise-wide discovery informatics framework for comprehensive and successful discovery research. We are an international business headquartered in San Leandro, CA, with offices worldwide. MDL Information Systems, Inc. is a wholly owned subsidiary of Elsevier Science, Inc. For more information about MDL, please visit www.mdli.com.

Sigma-Aldrich is a leading Life Science and High Technology company. Our biochemical and organic chemical products and kits are used in scientific and genomic research, biotechnology, pharmaceutical development, the diagnosis of disease and chemical manufacturing. We have customers in life science companies, university and government institutions, hospitals and in industry. Sigma-Aldrich operates in 33 countries and has over 6,000 employees providing excellent service worldwide. We are committed to the success of our Customers, Employees and Shareholders through leadership in Life Science, High Technology and Service.

For more information about Sigma-Aldrich, please visit our award-winning web site at www.sigma-aldrich.com.

This release contains forward-looking statements relating to future performance, goals, strategic actions and initiatives and similar intentions and beliefs and other statements regarding the Company|s expectations, goals, beliefs, intentions and the like, which involve assumptions regarding Company operations and investments and conditions in the markets the Company serves. The Company does not undertake any obligation to update these forward-looking statements.