The Hawaii Community Studies on Pesticides has used methods developed by BEVENUE et al. (1966,1968) to determine pentachlorophenol (PCP) residues in human blood and urine. The PCP-blood method has also been applied to the determination of 2,4-D and dicamba in human blood and urine (RIVERS et al. 1970). The modified PCP analytical procedure described in this paper represents an efficient combination of features taken from the procedures previously used, plus the use of a mechanical mixing technique developed by THOMPSON (1970) for extractig organochlorine pesticides from human serum samples. The procedure retains the accuracy of the procedure previously used, requires less time and equipment to perform, and applies to both human blood and urine.