4-Phenylcyclohexene (4-PCH) is a by-product formed during the polymerization of styrene-butadiene latex used in carpet backing. Limited reports suggest that exposure to very low levels of 4-PCH or other emission products following new carpet installation may result in health complaints. Significantly, it has been claimed that Swiss-Webster mice held in neck restraints and exposed head-only to approximately 0.4 ppm 4-PCH for a few hours suffered severe toxicity including death. A 2-wk inhalation and neurotoxicity study was therefore conducted in Swiss-Webster mice using standard methods of toxicity testing. Groups of 40 mice were exposed to 0, 7, 18 or 71 ppm (near-saturated atmosphere) 4-PCH vapour, 6 hr/day for 9 consecutive days. Data were collected on a wide variety of clinical, neurological and histopathological parameters including extensive neurohistopathology. All animals survived the exposures, and there were no treatment-related effects. Because of the occurrence of spontaneous lesions in two high-dose group mice, 40 additional males were exposed to 0 ppm or a near-saturated atmosphere of 4-PCH under the same exposure regimen. No treatment-related lesions were observed in the follow-up study, confirming the conclusions of the original study. These findings, consistent with the reported lack of toxicity of inhaled 4-PCH in rats, do not suggest a direct, organic, association between low-level 4-PCH exposure and human complaints. Further, the results of this study suggest that positive findings in mice may have been due to methodological problems and not to exposure to 4-PCH.