In view of the growing demand in Poland for the determination of trace amounts of mercury in blood the cold vapour atomic absorption method has been adapted and modified. The described method is characterised by: precision - 4% at a level of 80 ng Hg; sensitivity - 10 ng Hg; detection limit - 15 ng Hg in a sample, i.e. about 3 ng Hg/ml; recovery - 89.4% at a level of 49 ng, 97.8% at a level of 490 ng Hg. The method was used for the determination of mercury in blood in persons who had not been occupationally exposed, i.e. 63 adults (women and men) and 4 children. The mean value obtained for adults was 8.1 +/- 13.4 ng Hg/ml of blood, and more than 50% of samples contained mercury at a level of less than 20 ng Hg/ml of blood.