The report focuses on the qualitative profiles of genetic activity produced by 65 pesticides and our efforts to classify them according to their genotoxic effects and chemical structures. Three main categories may be distinguished based on the qualitative results: Category 1 pesticides were active in most of the in vitro and in vivo assays employed, category 2 compounds demonstrated fewer positive results, and category 3 pesticides gave negative results in all tests and represent structurally diverse compounds. Using the computerized profile matching methodology, from 2,080 possible pairwise chemical combinations of the 65 pesticides, 20 statistically significant pairs were selected. Six groups of pesticides were identified that were substantially similar to groups of pesticides formed previously (Waters et al., 1982) based on genetic activity and chemical structure. The matches showed excellent qualitative and, in most cases, excellent quantitative agreement. Hence, it appears that specific patterns of test results present in the genetic activity profiles are related directly to chemical structure.