1. Glucose 6-phosphate dehydrogenase from Eimeria stiedai does not reduce NAD or any of its analogs tested. It does reduce NADP and its thionicotinamide and 3-acetylpyridine analogs. 2. It will accept D-glucose as substrate, but not 2-deoxy-D-glucose, glucose 1-phosphate, or 2-deoxy-D-glucose 6-phosphate. 3. Its response to a number of compounds that activate or inhibit the enzyme from other organisms has been determined. 4. The molecular weight is ca. 240,000 by gel chromatography, and only one isoenzyme could be detected by disc electrophoresis. 5. The enzyme resists conditions that commonly cause dissociation to lighter weight active forms.