A 35-year-old furniture refinisher came to the occupational medicine clinic with complaints of upper respiratory irritation, fatigue, and lightheadedness occurring on a daily basis after using a methylene chloride-containing paint stripper. Determinations of blood carboxyhemoglobin (COHb) on three occasions showed an apparently linear elevation of COHb as a function of hours worked on the day of sampling. COHb levels predicted from spot industrial hygiene measurements were in close concordance with those observed in the patient, indicating the potential usefulness of COHb monitoring in estimating airborne exposure levels. Methylene chloride (or dichloromethane) is an organic solvent that has found wide use as a degreaser, paint remover, aerosol propellant, and a blowing agent for polyurethane foams, and as a solvent in food processing, photographic film production, and plastics manufacturing. Discovery of its unusual metabolic fate--conversion to carbon monoxide in vivo--has earned the compound a special place in the solvent toxicology literature. Demonstration of oncogenicity in experimental animals has occasioned a reconsideration of exposure limits, with emphasis upon stricter controls. In some workplaces, conditions prevail in which controls are inadequate to prevent even acute toxicity, much less long-term exposure risks.