Methylmercury in serum (S-MeHg) was assessed from serum concentrations of total (S-TotHg) and inorganic mercury (S-InoHg), determined by cold vapor-atomic absorption spectrometry. The samples were collected from 135 women on two occasions, in 1968-1969 and 1980-1981. In a subgroup of 29 women, an association was found between S-MeHg and the amount of fish consumed in 1968-1969 (r = 0.38, P = 0.04). The association was stronger (r = 0.50; P = 0.006) when the individuals' mean S-MeHg from 1968-1969 and 1980-1981 were plotted vs fish consumption 1968-1969. In the group, as a whole, there was an association between S-InoHg and number of dental amalgam surfaces, in both 1968-1969 (r = 0.48, P = 0.0001) and 1980-1981 (r = 0.57, P < 0.0001). The S-InoHg increased by approximately 0.1 nmol/L per amalgam tooth surface, corresponding to an uptake of approximately 0.2 microgram/day per amalgam surface, but with considerable interindividual differences. The levels were lower in 1980-1981 than in 1968-1969 for both MeHg and InoHg. The medians and ranges (nmol/L) were for MeHg 1968-1969: 3.6 (0.3-11.9); MeHg 1980-1981, 2.0 (-0.4-8.7); InoHg 1968-1969, 3.3 (0.7-11.8); InoHg 1980-1981, 1.7 (0.1-11.8); TotHg 1968-1969, 7.2 (1.9-18.8); and TotHg 1980-1981, 3.9 (1.0-14.2). The decrease in S-MeHg is probably due to a decreased consumption of MeHg via contaminated fish. The decrease in S-InoHg may reflect a decrease in environmental exposure, but the possibility of contamination of the 1968-1969 samples at sampling and/or storage cannot be excluded.