Plasmodium falciparum was cultivated with umbilical cord erythrocytes or with erythrocytes from human adults for 33 days and 50 days respectively. The erythrocyte infection rate increased eightfold to eighteenfold at intervals of three to four days, the highest erythrocyte infection rate being more than 20%. Furthermore, the infection rate of umbilical cord erythrocytes was higher than that of adult erythrocytes at 48, 72 and 96 hours of cultivation, respectively (P less than 0.01). The results suggested that human umbilical cord blood might be a good source of erythrocytes for in vitro cultivation of malaria parasite.