Intramuscular, intravenous, and subcutaneous injections of heroin, methadone, morphine, LAAM, cocaine, d-amphetamine, and phencyclidine produced about equivalent effects on schedule-controlled responding in rhesus monkeys. By the buccal route, potency was reduced by approximately three-fold except with cocaine and heroin; with cocaine, buccal potency was equivalent to the parenteral routes while with heroin, buccal potency was reduced by about 20-fold. By the oral route (gavage), methadone, morphine, heroin, and phencyclidine were at least 50–100 times less potent than by i.m., i.v., or s.c. routes. Cocaine was about sixteen times less potent orally than parenterally, while LAAM and d-amphetamine were only slightly less potent orally than parenterally. Thus, for certain drugs like methadone and phencyclidine, relative potencies by oral vs. parenteral routes in rhesus monkeys differ greatly from those obtained in humans.