The response of clinical blood values to graded levels of dietary aflatoxin was studied in three populations of chickens. Male chicks of two commercial broiler strains, one color-sexed and the other feather-sexed, and a randombred strain were fed dietary aflatoxin at levels of 0, 1.25, 2.50 or 5.0 microgram/g of diet from 1 to 21 days of age. At the conclusion of the 21-day treatment period, all remaining birds were bled by cardiac puncture and packed cell volume (PCV), erythrocyte counts (RBC), hemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), total plasma protein, and total plasma cholesterol were determined. All strains of broilers were susceptible to aflatoxicosis as detected by total plasma protein and cholesterol. Anemia associated with aflatoxicosis was induced in the two commercial broiler lines, but not in the randombred line. The PCV, RBC, and Hb were diminished from control values in a dose-related fashion by graded levels of aflatoxin in the commercial broilers, but not in the randombred line. Decreases in MCV with no significant changes in MCHC were observed in all strains.