A flow chart is presented as a recommended sequence of tests to predict the carcinogenic hazard, and to predict and quantify the mutagenic hazard to germ cells of chemicals to humans. Ten associated principles of testing for these endpoints are also suggested. These recommendations are the result of a meeting convened under the auspices of the International Programme on Chemical Safety (IPCS), as part of their project on 'Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals'. The meeting was held at Carshalton, Surrey, from 13-17 February 1995.