The neurotoxic properties of cyclohexane and n-hexane mixtures were assessed in rats. Animals were exposed for 22 hrs/day for 6 months to 7, 20, or 71 ppm of cyclohexane or cyclohexane in a mixture of C6 hydrocarbons, or to 123, 124, and 128 ppm of n-hexane or hexane mixtures. Neurotoxic effects seen with cyclohexane were consistant with effects from n-hexane or hexane mixtures (axonal swelling and age-related dystrophic axons of the medulla oblongata). No evidence was seen to indicate that cyclohexane, alone, was neurotoxic after 6 months of exposure. Summary reports provided the following information. A mutagenicity assayin Salmonella typhimurium tester strains TA98, TA100, TA1535, TA1535, and TA1538 exposed to concentrations of up to 5200 ug/plate f cyclohexane yielded negative results. Two mouse lymphoma L5178Y forward mutation assays found no increase in forward mutations at the TK locus for activated or non-activated systems. Sister chromatid exchange assays of 5 dose levels of cyclohexane in Chinese hamster ovary cells yielded negative results in both activated and non-activated test systems. An in vivo cytogenetics bone marrow cell assay in rats exposed by inhalation to 96.6 to 1041.6 ppm of cyclohexane for 6 hrs/day on 5 consecutive days yielded negative results. Two-generation reproduction and teratology studies of toluene were conducted in rats exposed by inhalation to concentrations of up to 2000 ppm. No embryotoxicity nor teratogenicity were noted, but at 2000 ppm there was maternal toxicity (not described) and slightly decreased fetal body weight.