To check the usefulness of the hair mercury value for evaluation of intake of mercury, total mercury in red cells and organic mercury in hair were measured and compared on islanders whose fish consumption varied to a considerable extent. On both the male and female, correlations of these two mercury levels were significant. The slopes of regression lines did not differ between the male and the female, but the level of hair organic mercury was higher in the male than in the female. Age-differences were observed in the red cell-to-hair relationship of mercury, i.e. the age-group aged 50 and over had much milder slopes than the group aged 20-49 in both the male and the female. The importance of age-matching was mentioned.