[New data on the circadian cycle of Plasmodium. Preliminary note]

A frozen strain of Plasmodium yoelii nigeriensis is inoculated at 4 pm, midnight and 9 am onto inbred Mice. In all instances young gametocytes (type 0) appear in the blood only between 10 am and 6 pm. Although the erythrocytic schizogony occurs regularly during the whole circadian period, the latency increases progressively when the infective subinoculations are made at midnight, 4 pm and 9 am. Possibly, the infective merozoite can only enter the red blood cell around midnight.