A subchronic 90-day study was conducted with chlorinated and non-chlorinated humic acids with male Sprague-Dawley rats. Body weight gain, terminal organ and body weights, food and fluid consumption, clinical chemistries, hematological parameters, and urinalyses were determined for all animals. Selected organs were examined microscopially. Significant findings were confined to those rats given the high dose of chlorinated humic acid (1.0 g/L total organic carbon). The terminal body weight and average weekly body weight gain were significantly lower (p < 0.05) in the high dose group as compared to the distilled water control group. The difference can be partially explained by a 16% lower daily fluid consumption. The average weight of the kidneys was significantly higher in the high chlorinated humic group as compared to controls. Hematological parameters and clinical chemistry values were normal in all treatment groups. The most significant finding was the increased incidence and severity of hematuria in the high dose chlorinated humic acid group.