A number of substituted phthalimide, 1, 8-naphthalimide, succinimide and glutarimide derivatives demonstrated significant hypolipidemic activity at 20 mg/kg/ day, I.P. after 16 days dosing. The N-(n-pentyl) succinimide proved to be the most potent analogue of the new compounds, lowering serum triglyceride levels 51 % and serum cholesterol 47 % after 16 days dosing in mice. For the N-substituted derivatives, i. e., n-butyl, butanone, and propionic acid, of these four cyclic imides, there appeared to be no obvious trend in ability to reduce serum lipid levels. In general, the 1,8-naphthalimide and glutarimide derivatives appeared to be less active than phthalimide and succinimide. However, the α-phenylsuccinimide afforded less activity than the α-phenylglutarimide. Most of the derivatives at 20mg/kg/day demonstrated improved activity over clofibrate at 150mg/kg/day.