Male mice of Kunmlng strain were infected with 10 000 tachyzoites intraperitoneally. 2 hours after infection the mice were divided into 2 groups and administered 5 % of amylurn and 200 mg/kg of artemether by gavage for 8 consecutive days. The ultrastructural enzyme cytochemical studles on cytidine monophosphatase (CMP ase) and glucose-6-phosphatase (G-6-P-ase) of the parasites were carried out. CMP-ase was found scattered in the lysosomes of the parasites as well as in the macrophages. No differences were observed in the localization and intensity of CMP-ase activity between the nontreated and treated with drug parasites. G6-P-ase was found surrounding the parasite membrane and scattered in the parasitophorous vacuole in the nontreated parasites. After treatment with artemether, the intensity of G-6-P-ase activity was decreased compared with nontreated control parasites. It is suggested that artemether may exert some action on the G-6-Patase of T. gondii and thus influence the energy metabolism of the parasite.