4-Chloro-3-nitroaniline was given to groups of 20 male and 20 female rats by gavage at doses of 3.6, 18, or 90 mg/kg in a 10% corn oil suspension. Doses were administered 5 days per week for 90 days. The high dose resulted in reduced body weight gain in males, reduced feed consumption and fluctuating feed consumption in both sexes, slight hemolytic anemia with Heinz bodies in both sexes, enlargement of the spleen due to congestion, hemosiderosis, and increased extramedullary hematopoiesis in both sexes, inflammatory changes in the splenic capsules of two females, hemosiderin pigmentation of the liver in both sexes, bone marrow hyperplasia in both sexes, increased liver weight in females, and testicular atrophy. The middle dose produced a fluctuating feed consumption pattern in males, Heinz bodies in both sexes, very slight anemia in females, splenic hemosiderosis in males, slightly increased splenic extramedullary hematopoiesis in females, hemosiderin pigmentation of the liver in males, and possibly increased liver weight in females, and inflammatory changes in the splenic capsule of one male. The low dose produced Heinz bodies in males and possibly females although the Heinz body counts of females were not statistically significant. The primary toxicologic damage produced by 4-chloro-3-nitroaniline is hemolytic or Heinz body anemia and testicular atrophy. Thus the toxicity of 4-chloro-3-nitroaniline is similar to that of other aromatic nitro and amino chemicals.