Abstract: A combined regimen of PAC was studied in rhesus monkey infected with Plasmodium cynomolgi. Monkeys infected by blood transmission were rapidly cured after combined treatment with PAC once daily for 3 days. In the observation period asexual parasites reappeared only once or twice, wich might be short-term relapses, in animals infected by sporozoites. On the other hand, much more frequent parasite reappearance occurred in animals treated with chloroquine alone or PAC in one day course.According to the assumption of "hypnozoite" in sporozoite-induced infection, long-term relapses would be expected after the primary onset and a period of negative parasitemia. However, it was not confirmed in this study, as no long-term relapse was detected in animals followed for more than 300 days.Side effects occurred mainly in the gastro-intestinal tract of monkeys receiving a 3-day course of PAC.