Ten compounds representative of diverse classes of chemicals were evaluated for their cytotoxicity and transforming ability to human skin fibroblasts in vitro. Only five of the ten compounds were highly cytotoxic in the 0-100 micrograms/ml range and their order of cytotoxicity was: 2,5-bis(1-aziridinyl)-3,6-bis(carboethoxyamino)-1,4-benzoquinone (AZQ) greater than cis-platin greater than bis(chloromethyl)ether (BCME) greater than acrylonitrile greater than aflatoxin B1 (AFB1). The other five compounds, aflatoxin B2 (AFB2), methylmethacrylate, 1-naphthylamine (1-NA), 2-naphthylamine (2-NA), and cyclophosphamide, exhibited less than 40% inhibition of colony formation even at 100 micrograms/ml of the compound (the maximum concentration of AFB2 used was 50 micrograms/ml due to its low solubility). Anchorage-independent growth of exposed cells in soft agar was used as a biological endpoint for the expression of chemical transformation. AFB1 had strong transforming ability, whereas AFB2 was a weak transforming agent. The transforming abilities of acrylonitrile, AZQ, BCME, cis-platin, methylmethacrylate and 2-NA ranged between those of AFB1 and AFB2. 1-NA also induced the soft agar growth property in the treated cells even though this compound has not been shown to be carcinogenic. AFB1, AZQ, cis-platin, cyclophosphamide and 1-NA exhibited a dose dependent increase in soft agar growth frequency for at least three consecutive concentrations. The data suggest that anchorage-independent colony forming ability of exposed cells is a reliable marker to measure the carcinogenic potential of various hazardous chemicals.