Various chlorohydrocarbons found in industrial waste effluents, including chloroform (CHC13) and carbon tetrachloride (CCl4), can eventually contaminate public drinking water supplies. The present study was designed to evaluate the interaction between orally administered CHCl3 and CCl4 at hepatic and renal toxic threshold doses in male, Sprague Dawley rats. CHCl3 was administered by oral gavage once daily for 3 days Prior to sacrifice at 0, 0.1, 0.5 and 1.0 mmole/kg/day by itself or in combination with CCl4 at 0.1, 0.5 and 1.0 mmole/kg (administered by oral gavage 16 hr prior to sacrifice). The severity and frequency of hepatocellular damage increased in a dose-related manner with CCl4 and to a lesser extent with CHCl3 when they were administered individually. Renal damage was most evident in the highest CHCl3 dose group. Histopathology and serum enzyme data indicated that hepato-toxicity was greater than additive when CCl4 and CHCl3 were given in combination.