The leaves of the Catha edulis plant (Khat) are chewed extensively by inhabitants of several African and Arab countries. It has been postulated that the behavioral effects of Khat are similar to those of amphetamine and that one of its components, cathinone, is the principal active alkaloid. In the first study, the ability of i.v. l-cathinone (0.0008-0.05 mg/kg/infusion), dl-cathinone (0.0016-0.1 mg/kg/infusion) and d-amphetamine (0.0016-0.025 mg/kg/infusion) to maintain responding under a fixed-ratio 10 schedule of delivery was determined. All three drugs functioned as positive reinforcers. Relative to amphetamine, lower doses of l-cathinone maintained responding, whereas the function for dl-cathinone was shifted to the right of amphetamine. However, potency comparisons are complicated by the fact that the dose-infusion functions for both l- and dl-cathinone were broader and peaked at higher rates than those generated by d-amphetamine. Because response rates under ratio schedules of drug delivery are determined by several properties of a drug, the relative potency of cathinone and d-amphetamine was investigated further. In a second experiment, the effects of i.v. l- and dl-cathinone (0.025-3.2 mg/kg) and d-amphetamine (0.0125-1.6 mg/kg) on responding maintained under a multiple fixed-ratio 30 fixed-interval 5-min schedule of food delivery were determined in three monkeys. Although there were some increases in overall rats, these drugs primarily produced dose-dependent decreases in responding under both schedules. d-Amphetamine was 2 to 4 times more potent than l- and dl-cathinone which were equipotent. This may indicate that the lower rates of responding maintained by d-amphetamine in the first experiment were due to its greater potency in disrupting responding.