2,6-Dinitrotoluene (2,6-DNT) and pentachlorophenol (PCP) are used for industrial purposes and are found in the environment as hazardous contaminants. Because concurrent exposure to both compounds can occur, it is of interest to determine if organochlorine compounds potentiate the effect of nitroaromatic chemicals. CD-1 mice were treated with PCP (42.8 mg/kg) for 4 weeks. On weeks 1,2, and 4 after the initial PCP dose, mice were treated p.o. with 2,6-DNT (75 mg/kg) and 24 hr urines were collected. After concentration, the urines were tested for their mutagenic activity in Salmonella typhimurium strain TA98 without metabolic activation in a microsuspension bioassay. A significant increase (P < .05) in mutagenicity was observed in urines from mice treated with 2,6-DNT alone and in combination with PCP. By week 4, mice that received both 2,6-DNT and PCP excreted urine that was more mutagenic than that from animals which received only 2,6-DNT. At weeks 2 and 4, mice were sacrificed and intestinal enzyme activities (nitroreductase, azo reductase, Beta-glucuronidase, dechlorinase, and dehydrochlorinase) were quantitated. (Copyright (c) 1991 Wiley-Liss, Inc.)