Samples of red blood cells (RBCs) from 1178 inhabitants, consisting of 546 males and 795 females (over 40 years old), of a coastal town near Minamata City were analyzed for total mercury. The mercury concentrations in the RBCs showed lognormal distributions for both sexes with higher values in males than in females. The geometric mean of the mercury concentrations in the RBCs was 27.5 ng/g (ranging from 8.0 to 69.1 ng/g) for males and 20.4 ng/g (ranging from 7.0 to 63.7 ng/g) for females. The mercury concentrations in the RBCs decreased with advancing age. A significant regression between the geometric mean of the mercury concentrations in the RBCs and age was obtained for both sexes. The mercury concentrations in the RBCs from male inhabitants of the coastland area were significantly higher than those from male inhabitants of the inland area. In terms of occupation, the highest mercury concentrations were observed in the RBCs from fisherman. No significant difference in the present mercury concentrations in the RBCs was observed between the cases with Minamata disease and the controls.