We investigated the background levels of total mercury in blood and urine samples from Japanese subjects without occupational exposure to mercury vapor. Blood and urine specimens were decomposed in sealed Teflon containers, and total mercury concentration was measured by reductive vaporization-gold amalgam capture-atomic absorption spectrophotometry. The mean total mercury concentration in the blood of 56 women aged 34-65 was 18.2 +/- 9.9 ng/ml (range 3.9-56.8 ng/ml). The mean total mercury concentration in the urine of 130 men aged 22-39 was 2.33 +/- 1.50 micrograms/l (range 0.27-10.26 micrograms/l). The mean total mercury concentration in urine adjusted by specific gravity was 2.19 +/- 1.15 micrograms/l (range 0.68-7.68 micrograms/l), and that adjusted by creatinine was 1.51 +/- 0.68 micrograms/g creatinine (range 0.39-4.21 micrograms/g creatinine). These concentrations did not differ greatly from those reported from Europe and Japan. In expressing the total mercury concentration in urine, the creatinine-adjusted range between the minimum and maximum values was smaller than the range adjusted by specific gravity.