Total mercury (Hg) was determined in milk, eggs, beef, pork, human head hair, soil and water obtained from four geographical areas of North Dakota. The sampling areas were selected on the basis of differences in prevalent agricultural practices, climate and topography. Statewide average Hg concentrations in ppb were milk, 0.8; eggs, 12; beef muscle, 5; beef liver, 10; pork muscle, 11; pork liver, 15; head hair, 1708; soil, 30; rainwater and well water, less than one. There were no significant differences observed among areas in Hg content of any substance sampled except beef muscle. Beef muscle obtained from areas 2 and 4 contained significantly (P less than or equal to 0.05) higher levels of Hg than beef muscle from the other two areas. However, the magnitudes of differences were small (4 to 6 ppb). Considerable variation among individual beef and swine were noted but only six beef of 453 sampled and three swine of 156 sampled had tissue Hg exceeding 50 ppb. Appreciable variation was observed in Hg in eggs with respect to farms within an area, eggs from the same farm, and sampling times within a year. Few eggs sampled contained more than 50 ppb. Significantly (P less than or equal to 0.01) higher levels of Hg were found in head hair of women as compared with men and relatively large differences among individuals were observed. Average Hg in hair was generally low irrespective of sex of donor or area of the state as compared with data given in the literature. Soil Hg levels were consistently low in all areas of the state, and no relationship between cropping practices and soil Hg was detected.