The C-QSAR program is used to develop and search a database of over 18,000 equations that relate biological or physico-chemical properties of molecules to various molecular descriptors. The data used to derive the quantitative structure activity relationships (QSAR) are taken from various high quality journals. C-QSAR comprises two databases, one for structure-activity information biological systems (n = 9200) and the other for physical organic systems. Users can search the data in 20 different fields; for example by structure or substructure of the compounds involved, by the type of property correlated, by molecular properties, or by properties of the QSAR equation. Various ways in which information can be obtained is briefly discussed. Initially the database is often used for data mining, to search lead molecules, for substituent selection and "model mining" for lateral validation. The regression analysis is useful when the user wants to derive a new QSAR using his structures and activity data.