The survey of simian malaria in Japan which had been conducted since 1965 showed that no Japanese monkeys (Macaca fuscata fuscata and Macaca fuscata yakui) were infected with malaria parasites. Most interestingly, however, Babesia sp. was found in 4 (4.3%) of 93 Macaca fuscata yakui which had been reared in a monkey park. As for the monkeys imported from abroad, Plasmodium was only found in Macaca irus from Southeast Asia, namely, P. inui (14.1-25.0%), P. cynomologi (0.6, 3.2%) and P. coatneyi (4.3%) from various countries. On the other hand, Hepatocystis kochi was found in high proportion in Cercopithecus aethiops from Uganda. Two other blood sporozoa identified as H. semnopitheci and Entopolypoides macai were also seen in Macaca irus imported from Southeast Asia.