Rats were infected with Plasmodium berghei sporozoites, and 47, 51, and 57 hr later exoerythrocytic parasites were examined by electron microscopy. At 47 hr, approximately 30% of nearly mature exoerythrocytic parasites were degenerating and were surrounded by a cellular infiltrate of Kupffer cells, monocytes, monocyte-derived macrophages, and neutrophils. Neutrophils appeared to be actively ingesting electron-dense fuzzy parasite material which was normally present in the parasitophorous vacuole. By 51 hr other mononuclear cells penetrated with filopodia between the host hepatocyte and exoerythrocytic parasite, and directly into the exoerythrocytic parasite. Exoerythrocytic parasites that formed merozoites at 51 hr lacked any notable cellular infiltration.