The application of statistical periodic analysis confirms the existence of significant periodic fluctuations in the mortality of mice infected with a rodent malaria(Plasmodium berghei). The mice were obtained from a single commercial breeder and were kept under strict controlled environmental conditions. The duration of the study was five years. The infection was induced by weekly mouse‐to‐mouse passages of infected blood. The cumulative mortality at day 7 after the infection of each weekly passage was used for the study variable.