RU 25591 (6, 7, 8, 9-tetrahydro N, N-dimethyl 5-[4-nitrophenyl] oxy 5H-benzocyclohepten 7-amine) cis, fumarate a potent, selective and long acting serotonin uptake inhibitor was examined for anorectic properties. It was found that RU 25591 reduced food intake in rats, dogs and pigs. Kinetics in single dosed animals showed that the duration of RU 25591 food intake depression was shorter than in vivo serotonin uptake inhibition. In repeated dosing treatment a progressive time- related decrease in the inhibition of food consumption was observed which was more evident in pigs than in dogs. The anorectic activity of RU 25591 does not depend exclusively on its ability to block 5HT uptake. However available biochemical results do not enable us to understand its possible mechanism of action which is not classical and remains to be clarified in further experiments.