Failure to detect hypnozoites in hepatic tissue containing exoerythrocytic schizonts of Plasmodium knowlesi.

Sections of paraffin-embedded rhesus liver containing numerous nearly mature exoerythrocytic schizonts of the non-relapsing malaria parasite, Plasmodium knowlesi, were examined for the presence of hypnozoites by indirect immunofluorescence, employing both homologous and strongly cross-reacting heterologous sera. No hypnozoites or evident hypnozoite equivalents were detected in tissue which, by analogy with results obtained for the relapsing species, P. cynomolgi bastianellii, should have contained 35--50 of the uninucleate forms. These observations are presented as additional evidence in favor of the hypnozoite theory of malarial relapse.