Uracil was administered to male and female dogs for 3 months and to male dogs for 12 months at dose levels of 0, 210, 420, 840 and 1680 mg uracil per kg body weight per day by gavage. While there were minor differences seen in food consumption, water consumption and erythroid parameters between the 3-month and the 12-month studies, it was concluded that there were no adverse effects seen on these parameters nor on body weight, EKG, clinical laboratory studies and organ weights. Pathological observations did not show treatment-related effects.