Administration of clofibrate to adult mice (20-25 mg of clofibrate/day) increased liver glycerophosphate acyltransferase (EC 2.3.1.15) activity by 2.3-fold within 24 h. This increased glycerophosphate acyltransferase activity was mainly localized in the liver microsomal fraction. Three other hypolipidemic drugs, i.e. Bezafibrate (Boehringer Mannheim Co.), Gemfibrozil (Warner-Lambert Co.) and Wy-14,643 (Wyeth Laboratories), when fed to mice, also increased the liver glycerophosphate acyltransferase activity by 2-3-fold in 24 h. Simultaneous administration of inhibitors of protein biosynthesis, such as cycloheximide or actinomycin D completely abolished such stimulation of liver glycerophosphate acyltransferase by clofibrate.