Thirty-seven synthetic chemicals plus two mycotoxins were tested for mutagenicity in an Arabidopsis embryo system. The results of this test, prokaryotic repair tests, bacterial mutation assays, eukaryotic cell systems, and in vivo tests were compared to the carcinogenicity classifications of the chemicals. Thirty-two of the thirty-seven chemicals tested were correctly identified as either mutagenic or nonmutagenic in the Arabidopsis assay. To compare these results with those of the other assays, the authors defined three criteria. 'Sensitivity' indicated the percentage of tested carcinogens that were mutagenic in a system. Of 20 carcinogens tested in the Arabidopsis assay, 19 were mutagenic (sensitivity 95%). For the other assays, sensitivities ranged from 16% to 88%. 'Specificity' indicated the percentage of noncarcinogens that were nonmutagenic in a system. Three of the twelve non-carcinogens were nonmutagenic to Arabidopsis (specificity 25%).