NIOSH recommends in this document that employee exposure to hydroquinone (123319) be limited to 2.0mg/m3, about 0.44 parts per million, as a ceiling concentration during a 15 minute collection period. Recommendations were provided for medical surveillance steps, environmental monitoring, labeling and posting of hazards, use of personal protective clothing and equipment, instructing employees of potential hazards, safe work practices, waste disposal, confined space entry requirements, monitoring, recordkeeping, and emergency procedures. Evidence was presented of eye injuries, systemic effects and dermal irritation following exposure to hydroquinone. However, no eye injuries have been documented in the absence of quinone vapor. No studies were available of the morbidity and mortality among persons working with hydroquinone, of the effects of exposure to hydroquinone by inhalation, or of teratogenic actions caused by exposure of pregnant animals or women to hydroquinone. Hydroquinone appears to effect the mitotic process in unicellular organisms and to decrease reproductive success in mammals; no evidence of mutagenicity in organisms other than bacteria and yeasts had been presented.