The dose response relationship between tobacco consumption and melanin pigmentation in the attached gingiva was examined on two occasions 4 years apart in a group of Japanese lead workers with blood lead concentrations below 2.0 mu mol/kg (40 micrograms/100 g). In the two examinations, 12% and 18% of the total group of workers and 17% and 24% of the smokers had melanin pigmentation. The prevalence of pigmentation was significantly higher in smokers who inhaled more than 10 cigarettes per day (17% and 25%) than in nonsmokers (0% and 2%), and tended to increase significantly with tobacco consumption. Lead absorption was not associated with melanin pigmentation.