A number of substituted amine-carboxyborane esters were examined for their hypolipidemic activity in rodents. Trimethylamine-carbomethoxyborane, Me3NBH2C(O)OMe, was observed to be the most effective hypolipidemic agent in the rodent at the low dose of 8 mg/kg/d. This agent effectively increased the high density lipoprotein (HDL) cholesterol content and lowered the low density lipoprotein (LDL) cholesterol and triglyceride contents of rat lipoproteins. Furthermore, the agent accelerated cholesterol excretion from the body of the rat and reduced the activity of the rate-limiting enzyme involved in the de novo synthesis of lipids in the liver. The agent has a safe therapeutic index, and appeared to have more promise as a therapeutic agent than other borane esters.