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The relative amounts of the ali-esterases in beef and rabbit kidney and liver homogenates have been evaluated quantitatively, after resolution of the esterases by starch-gel electrophoresis. The relative amounts of total ali-esterases in livers and kidneys of a number of animals and fowl have been determined. The data presented and other unpublished data show that the ali-esterase content of tissues increases with age and that there is a sex difference.

DDT (100 p.p.m.) was added to the diet of female rats that were then bred to males receiving the same diet. Liver carboxylesterase and liver and kidney vitamin A levels were measured in the dams and their young at parturition and at weaning.DDT did not have any adverse effect on the breeding performance of the adults or on the vitamin A stores of the newborn or weanling rats. Vitamin A stores of the dams were reduced by the pesticide. Liver carboxylesterase increased greatly between birth and weaning and remained almost constant thereafter. DDT caused a marked increase in liver carboxylesterase over and above that which occurred during growth.

Mats sf different ages were fed a diet containing 10 p.p.m. parathion with or without vitamin A supplementation for various periods of time, and the effects on liver and kidney carboxylesterases were measured.Marked inhibition of carbsxylesterases was observed shortly after the parathion diet was introduced. The degree of inhibition was not altered appreciably by continued feeding of the diet containing parathion. Young female rats showed some recovery of liver carboxylesterases on continued feeding of the parathion diet. After removal of vitamin A from the diet, the levels of liver carboxylesterases of male rats fed parathion increased appreciably.