The enzyme activity of Mg++-ATPase, Na+-K+-ATPase, 5'-nucleotidase and NAD(P)H-oxidase was cytochemically detected at the ultrastructural level in mouse peritoneal macrophages infected with untreated and with specific antibody-coated Toxoplasma gondii tachyzoites. The Mg++-ATPase and 5'-nucleotidase were distributed throughout the macrophages' plasma membrane but were not observed in the membrane lining endocytic vacuoles containing ingested parasites; however, Na+-K+-ATPase activity was detected in the macrophages' plasma membrane as well as in the parasitophorous vacuoles that contained untreated or specific antibody-coated parasites. Reaction product, indicative of NAD(P)H-oxidase, was detected in the parasitophorous vacuoles that contained only specific antibody-coated parasites.