Pigeons were trained to peck a red or green center key 15 times to turn it off. After a delay, 2 side keys, 1 red and 1 green were illuminated. Pecks on the side key whose color matched the color that the center key had been produced food. Pecks on the other side key produced a timeout. The effects of various drugs were studied as the delay between extinguishing of the center key light and illumination of side keys was varied from 1-8 s. Pentobarbital and phencyclidine consistently decreased matching, but morphine, d-amphetamine and .DELTA.9-tetrahydrocannabinol had little effect on matching even at doses that increased latency to respond and decreased the rate of responding. Pentobarbital frequently decreased matching at doses below those that increased response latency and decreased response rate, but phencyclidine decreased matching only at doses that increased latencies and decreased rates. The effects of pentobarbital on matching did not depend on the delay duration.