Thirty female beagle dogs, 7 to 8 months old, were assigned to five groups. Control, low dosage, medium dosage, high dosage, and pair-fed groups were offered 0, 1, 2, 4 and 0 mg of sodium arsenite per killigram of body weight per day (mg/kg/day), respectively, in their feed. On Day 59, the dosage was doubled for the rest of the experiment, which ended on Day 183. Nominal dosages of 4 and 8 mg/kg/day caused a significant decrease in feed consumption. The initial decreased feed consumption was followed by increased intake over time. Nominal dosages of 4 and 8 mg/kg/day caused a significant decrease in body weight. Body weight loss of high dosage and pair fed groups were not significantly different. Serum aspartate aminotransferase was elevated in dogs exposed to 4 and 8 mg/kg/day of sodium arsenite. Serum alanine aminotransferase was elevated in dogs exposed to 2, 4, and 8 mg/kg/day. No gross or light microscopic lesions were present in the liver of any group. This study shows that dietary sodium arsenite causes a dose-dependent decrease of feed consumption and body weight. Weight loss is caused by decreased feed consumption, not by the direct effect of the sodium arsenite.