The Developmental Therapeutics Program (DTP) has operated a repository of synthetic and pure natural products which were evaluated as potential anticancer, and more recently, as anti-HIV, agents for more than 40 years. The repository is run by a NCI contractor and has an historic inventory of greater than 600,000 compounds which have been supplied over the years to DTP from a variety of sources world-wide. These materials, not based on "proprietary" framework, represent unique structural diversity. The collection contains both synthetic compounds and fully characterized pure natural products.