The effects of acute poisoning by cupric sulfate in a number of species are well known; however, the effects of chronic low-level ingestion of cupric sulfate are less well characterized. Because exposure of humans to cupric sulfate may occur through drinking water, food, soil, or ambient air, subchronic toxicity studies were conducted in male and female F344/N rats and B6C3F1 mice by the drinking water (2-week exposure) and dosed feed (2- and 13-week exposure) routes. Animals were evaluated for histopathology, clinical pathology, reproductive toxicity, and tissue metal accumulation, and target organs were examined by a variety of special stains and by electron microscopy to characterize the observed lesions. In drinking water, cupric sulfate concentrations of 300 to 100 ppm produced no ill effects, whereas concentrations of 3000 to 30,000 ppm were lethal to rats and mice within 2 weeks. In feed, cupric sulfate concentrations of 4000 to 16,000 ppm caused significant reductions in body weight gain in both species in the 2- and 13-week studies. Hyperplasia and hyperkeratosis of the limiting ridge of the forestomach were present in both species in the 2- and 13-week studies. Rats in the dosed feed studies had a dose-related increase in inflammation in the liver and changes in clinical chemistry parameters which were indicative of hepatocellular damage and cholestasis. Histologic changes in the kidneys of rats consisted of a dose-related increase in the number and size of eosinophilic protein droplets in the epithelial cytoplasm and the lumina of the proximal convoluted tubules. Droplets were larger and more numerous in males than in females. Urinalysis results were suggestive of renal tubular epithelial damage. Iron staining of spleens from treated animals indicated a marked depletion of iron stores in both male and female rats, but not in mice, while hematologic and clinical chemistry alterations in rats in the 13-week study, along with histologic changes in bone in the 2-week dosed feed study, were indicative of a microcytic anemia. Cupric sulfate produced no adverse effects on any of the reproductive parameters measured in rats or mice of either sex. These results indicate that cupric sulfate at high exposure levels is a hepatic and renal toxicant, as well as an inducer of anemia in rodents, with rats more sensitive than mice following subchronic exposure.