Abstract. Organochlorine pesticide concentrations in blood and various clinical test variables were measured in 2,620 pesticide-exposed subjects and in 1,049 persons not occupationally exposed to pesticides. Differences in the pesticide contents of blood were identified in relation to geography, age, and occupational exposure. Analysis of hematologic and biochemical variables in terms of broad occupational categories revealed only very limited differences, but relationships of certain biochemical tests to serum organochlorine pesticide contents suggested subtle effects of these pesticides on liver function.Beginning in 1965, the U.S. Public Health Service established Community Studies in 14 states