For 24 agents classified by the International Agency for Research on Cancer as known or suspected human carcinogens, we previously catalogued the qualitative genetic bioassay data available in the literature. In the present analysis, dose information, where available, was added to this data base: either the lowest effective dose (LED) or the highest ineffective dose (HID) was recorded for each agent and bioassay system. Bioassay systems were organized according to classes of genetic activity and subdivided by the phylogenetic level of the test organism. For each compound, the quantiative results in the test systems were represented by computer-generated bar graphs ('genetic activity spectra'). The x-axis unit values corresponded to the 100 different systems, and the y-axis values were the logarithmically transformed LED or HID values. Statistical methods and pattern-recognition techniques were used to evaluate the genetic activity spectra. Spectra were compared among agents grouped according to target-organ specificity. In addition, the spectra of all possible pairs of compounds were compared to identify compounds displaying qualitatively or quantitatively similar genetic activity. Chemically similar compounds frequently produced similar spectra of genetic activity, and it was possible to identify the most appropriate test systems for some classes of compounds. As the data base for human carcinogens is enlarged, analysis of genetic activity spectra may contribute to our understanding of the structure-activity relationships and mechanisms of action of these agents. (Copyright (c) 1984, Elsevier Science Publishers B.V.