A total of 168 broiler chickens (6 to 9 weeks of age) and 192 turkey poults (3-1/2 to 6-1/2 weeks of age) were fed purified zearalenone at levels of 0 (control), 10, 25 (turkeys only), 50, 100, 200, 400, and 800 mg/kg diet for a 3 week period to evaluate its toxicity. Dietary zearalenone had no effect on body weight gain, feed consumption, weights of liver, heart, spleen, and bursa of Fabricius, serum calcium, phosphorus, alkaline phosphatase, total protein and cholesterol, hematocrit, hemoglobin, red blood cell count, white blood cell count, and differential leukocyte count in both chickens and turkeys. Male broiler comb and testes weights were reduced by high levels of zearalenone. Female comb weight, broiler oviduct weight, and turkey testes and ovaries were unaffected by zearalenone. Histopathological examination of tissues revealed no change due to zearalenone. Male turkeys fed 400 and 800 mg/kg zearalenone had increased development of dewlaps and caruncles and exhibited considerable strutting behavior. Muscle and fat tissue from broilers fed 800 mg/kg zearalenone had no detectable estrogenic activity as measured by mouse uterine bioassay. These studies indicate that the effects of dietary zearalenone on finishing broilers and young growing turkey poults are minimal.