8 antioxidants were tested in the SOS chromotest for induction of SOS function and for modulation of benzo[a]pyrene-induced SOS function. None of the antioxidants leads to increased beta-galactosidase activity by itself. Butylated hydroxytoluene at concentrations between 10(-5) M and 3 X 10(-4) M enhances benzo[a]pyrene-induced SOS function at benzo[a]pyrene concentrations between 10(-6) M and 3 X 10(-5) M. Butylated hydroxyanisole, ethoxyquin, propyl gallate and octyl gallate also slightly enhance benzo[a]pyrene-induced SOS function at concentrations up to 3 X 10(-4) M though to a lesser degree than butylated hydroxytoluene. Dodecyl gallate, vitamin C and alpha-tocopherol do not increase benzo[a]pyrene action. In concentrations exceeding 3 X 10(-4) M all synthetic antioxidants tested but not vitamin C and alpha-tocopherol decrease beta-galactosidase activity both in the absence and, more extensively, in the presence of benzo[a]pyrene. Preliminary data suggest that the apparent suppression of benzo[a]pyrene-induced SOS function is not due to an effect on the formation of benzo[a]pyrene metabolites by the metabolizing system used.