Abstract: This paper reports the experiments in which tripynadine free base at a dose 4. 5 times that of ED50 was given to mice by intragastric administration. On the 20th day following the administration the mice were inoculated with 1 × 107 RBC infected with Plasmodium berghei ANKA strain. The infection rate was zero, implying that all mice had acquired protection. Although the residual activity time of tripynadine phosphate was longer than that of tripynadine free base or piperaquine phosphate, but tripynadine phosphate caused vomiting in monkeys during the medication. The residual antimalarial activity of tripynadine hydroxynaph-thoate was less than that of tripynadine phosphate or tripynadine free base. A total dose .of 200 mg/kg of tripynadine free base ensured residual antimalarial activity against P. cynomolgi bastianellii for 20 days. However, the residual activity decreased evidently when the total dose was reduced to 100 mg/kg. In short, it seems that the residual antimalarial activity of tripynadine free base is slightly less than that of piperaquine in monkeys.