Benidipine hydrochloride, a dihydropyridine calcium antagonist, decreases body weight and also has a hypotensive effect. The mechanism of its inhibitory effect on body weight is unclear, although this agent increases blood flow in brown adipose tissue, which functions as a main thermogenic organ. The hypothesis that benidipine hydrochloride activates brown adipose tissue to induce body weight loss was tested on mice made obese by pretreatment with monosodium-L-glutamate (MSG). When benidipine hydrochloride was incorporated in the diet (1.0 mg per gram of food) for 4 weeks, binding of guanosine-5'-diphosphate in brown adipose tissue mitochondria was significantly increased. Body weight and body fat decreased in both MSG obese mice and in lean controls. Results support the hypothesis and suggest the possibility that benidipine hydrochloride may be useful for treating obese hypertensive patients.