Mercury concentrations in hair were related to fish-eating habits in a group of 50 people reported to have a high consumption of freshwater fish. Mercury levels in hair ranged from 0.3 to 10.8 mg/kg with a mean +/- SD of 3.2 +/- 2.3 mg/kg. The average mercury level in hair from men was significantly higher than that in hair from women (3.8 +/- 2.6 mg/kg versus 2.4 +/- 1.8 mg/kg. Seven individuals (14%) had levels above 6 mg/kg. In people with equal fish consumption, significantly higher mercury levels were found in the hair of those eating fish from lakes Mälaren and Vättern than in those eating fish from Lake Hjälmaren. It has been reported that fish from the latter lake contains approximately 0.2 mg/kg mercury, whereas fish from the other two lakes contains approximately 0.4 mg/kg. The mean mercury level in hair was higher in the group eating freshwater fish more than three times a week (greater than or equal to 500 g fish flesh/week) than in the group eating less, although the difference was of borderline significance. Within couples (n = 16) eating equal numbers of fish meals per week, the men had significantly higher levels (mean 3.7 mg/kg) than the women (mean 2.5 mg/kg). The results from the present study show that people with a high consumption of Swedish freshwater fish have elevated levels of mercury in their hair, when compared with previously reported levels in the hair of Swedish pregnant women.