We examined the mutagenicity of cigarette smoker's urine in 32 healthy male cigarette smoker and 37 healthy male non-smoker. Twenty-four-hour urine specimens were subjected to blue rayon extraction which selectively adsorb polycyclic compounds, after which the elutions were fractionated by carboxymethyl cellulose column chromatography for removing antimutagenic compounds. The mutagens were measured by using an S9-mediated Salmonella mutagenicity test on strain TA98. Compared with those with non-smokers, smokers' urine showed a significantly higher urinary level of mutagens in the acid-elutable and in the sum of all chromatography fractions. A similar tendency was also seen in the alkali-elutable fraction. The subjects were classified into three groups according to the number of smoked cigarettes. Heavy smokers, who smoked more than 20 cigarettes per day, showed a significantly higher urinary level of mutagens than both non-smokers and light smokers especially in the acid-elutable and in the sum of all chromatography fractions. Our findings suggest that smokers are exposed to a great amount of polycyclic carcinogens and mutagens by cigarette smoking. These results also suggest that urinary level of mutagens measured by using blue rayon extraction combined with carboxymethyl cellulose chromatography could be a good index for estimating the exposure to carcinogens and mutagens such as polycyclic compounds.