Abstract: Our previous report that the EE merozites of Plasmodium cynomolgi from Vietnam continuously released from the liver to the blood circulation was further demonstrated in this report.Monkeys were given pyronaridine 24mg/kg-d×6 after being inoculated intravenously with 32×105 sporzoites of P.cynomolgi.Thick blood film examination was conducted two times daily till the day when trophozoites were detected.Under the residual action of blood schizontocied,a special ring form parasitemia at low patasite-density was detected for more than 30 days.As the ring forms of P.cynomolgi were demonstrated to be susceptible to pyronaridine in our previous experiments,it might be infer red that these ring forms derived from EE merozites released not for once but continuously for 30 days or longer. Furthermore the special ring form parasitemia of infected monkeys after administration with M8132-derivative of dabequiae was also detected.We came to the conclusion just as in the case of pyronaridine.The variation in the ring form parasitemia was coincident with Verhulst model and might be described with the grey differential equation.The authors considered that the short-term relapse might be incuced by the later retease of EE merozoites which multiplied repeatedly in the blood after the drug was excreted and its action disappeared.