The mutagenicity of urine from a healthy population of young adult men (average age of 23 years), including 61 smokers and 107 nonsmokers, was investigated with the Salmonella/microsome test using the tester strain S. typhimurium TA98. In quantifying the assay, the use of dichloromethane was suitable for eluting the mutagenicity of smokers' urine from the XAD-2 resin column. We assayed mutagenicity in condensates of such dichloromethane eluates and found that the mutagenicity of smokers' urine was significantly higher than that of nonsmokers' urine. In the smokers' group, correlation coefficient between "the mutagenicity of the urine" and "the actual number of cigarettes smoked on the day of urine collection" or "the average number of cigarettes smoked per day" was statistically significant at 0.266 or 0.454, respectively. Our results suggest a correlation between the increase of mutagens in urine and smoking habits.