Specimens of either sex of the freshwater catfish Clarias batrachus were exposed to safe and sublethal concentrations of an organochlorine, gamma-BHC (2 and 8 ppm), and an organophosphorus compound, malathion (1 and 4 ppm), for 4 weeks during the vitellogenic phase of their annual reproductive cycle. The effects on total lipid and its various fractions, viz., free fatty-acids, monoglycerides, diglycerides, triglycerides, phospholipids, free cholesterol, and esterified cholesterol, were studied in the liver, plasma, gonads, and muscle. Except for elevated liver lipid in the male in response to malathion, no significant change in total lipid could be observed following pesticide exposure. However, various lipid fractions responded differently to two concentrations of the pesticides. Both pesticides affected the metabolism of nonpolar and less polar lipids alike. Malathion inhibited only mobilization of hepatic phospholipid to gonads but not its hepatic biosynthesis, whereas gamma-BHC reduced its synthesis in the liver as well. These pesticides seemed to restrict the conversion of esterified cholesterol into free cholesterol without affecting the biosynthesis of cholesterol as such. In both sexes, esterification of free fatty acids to acyl glycerides and their mobilization from liver to gonads seemed to be restricted as a result of pesticides action.