Barium Chloride dihydrate (BaCl2.2H2O) was given for 92 days to B6C3F1 mice and Fischer 344/N rats in their drinking water at levels of 0, 125, 500, 1000, 2000, and 4000 ppm. The no-effect level for this study was 2000 ppm BaCl2.2H2O in the drinking water. At 4000 ppm, daily consumption for mice was 436 to 562 mg/kg barium, up to four times more chemical than rats. Mortality ranged from 60 to 70% in mice and from 10 to 30% in rats in the 4000 ppm groups. Deaths in mice were associated with a treatment-related renal toxicity. Renal lesions in rats were much less severe than in mice and did not contribute to the treatment-related deaths seen in the high dose group. Body weights of both species and sexes in the 4000 ppm groups were lower than controls at 92 days. Male and female rats in treated groups exhibited higher serum phosphorus than controls. Serum sodium, potassium, and calcium levels in rats were unchanged by barium treatment, as were hematological values. In both species at 4000 ppm, motor activity, grip strength, and thermal sensitivity were marginally affected. These effects were probably secondary changes resulting from BaCl2 toxicity observed at this dose level. In a mating trial, no anatomical effects on offspring of rats or mice were seen. Rats receiving 4000 ppm exhibited marginal reductions in pup weights. No effects were seen on reproductive indices.