Summary1. Anti-appetite action of d-amphetamine, d-desoxyephedrine, pipradrol (Meratran) and methylphenidate (Ritalin) was tested in selected trained cats. The agents were given s.c., once prior to, and twice following presentation of food. 2. A delay in eating response of half hour or more appears at dose levels of 0.25 to 0.4 mg/kg with all 4 agents. At doses of 0.63-1.58 mg/kg food consumption was reduced by more than half and eating response delayed 10-30 hours. 3. The compounds inhibited also at 1 to 2 mg/kg dose levels the operant behavior (bar pressing for food reward) of unconditioned and conditioned rats. 4. No qualitative or quantitative differences were found among the 4 agents studied with regard to stimulation of motor activity, toxicity and anorexigenic action. 5. Site of action of the anorexigenic effect of the compounds is discussed and similarity of this and other effects of piperidine stimulants on one hand and of amphetamine excitants is stressed.