The SOS Chromotest on Escherichia coli strain PQ37 was used to detect DNA damage induced by 16 chemical compounds and urine samples from smokers and a non-smoking psoriatic patient treated with mineral coal tar. The results confirmed the strong SOS inducing activity of 2-aminoanthracene and benzo[a]pyrene with metabolic activation and N-methyl-N'-nitro-N-nitrosoguanidine, mitomycin C and 4-nitroquinoline-N-oxide without metabolic activation. A weaker response in the absence of microsomal enzymes was observed with hydroxyurea (only at high doses) and the soluble Cr(VI) compounds potassium chromate and potassium dichromate. No effect was observed with ampicillin, cadmium chloride, cyclophosphamide, griseofulvin, the insoluble Cr(VI) compound lead chromate, the soluble Cr(III) compounds chromium nitrate, chromium chloride, chromium potassium sulphate, and the chelating agent sodium nitrilotriacetate. Among the Cr(III) compounds only chromium acetate produced a low but significant increase of SOS inducing activity. Solubilization by nitrilotriacetate of genotoxic Cr(VI) from insoluble lead chromate was observed, whereas no interaction occurred between nitrilotriacetate and the soluble Cr(VI) and Cr(III) compounds. Using urinary XAD-2 extracts, we found the SOS Chromotest poorly sensitive to the mutagens present in urine from tobacco smokers which, on the other hand, were detected by the gene mutation assay in Salmonella typhimurium (Ames test). A urine sample obtained from a psoriatic patient, therapeutically treated with mineral coal tar, had a significant SOS inducing activity with and even without metabolic activation, whereas in the Ames test it was active only in the presence of metabolic activation.(ABSTRACT TRUNCATED AT 250 WORDS)