Abstract: 10 rhesus monkeys which had been exposed each to the bite of 98-169 Anopheles dims with heavy gland infection of P. cynomolgi were observed for the incidence and frequency of relapses within 6 months after infection.The prepatent periods were 7 or 8 days. Whenever parasitemia was overt, a dose of 20mg/kg of chloroquine base was given orally per day for 3 days. 7 out of 10 monkeys suffered 1-4 relapses. The incidence was similar to that (62.5%) obtained by inoculating isolated sporozoites (0.28-6.5 million) of the same species into rhesus monkeys as reported in our previous paper.