Dichloromethane (DCM) is a clear, waterwhite, non-inflammable liquid of high volatility and sweet aromatic odor. It is widely used as an industrial solvent. In considering its neurotoxicity the CNS-depressant effects of both narcotic and hypoxic action must be taken into account, hypoxia being induced by the established biotransformation of DCM to carbon monoxide (CO). In animal studies depression of motor activity has been observed at high vapor concentrations around 5000 ppm, whereas disturbances of sleep-patterns, namely a depression of REM-sleep, has been shown down to 1000 ppm. Slowing of peripheral nerve conduction velocity occurred after DCM-injections giving rise to COHb between 4 and 6.8%. Controlled human exposure-studies revealed signs of CNS-depression, namely disturbances of psychomotor performance at 800 ppm, depression of the flicker fusion threshold and of vigilance performance down to 300 ppm, as well as performance decrement in a combined tracking-monitoring task at 200 ppm. Comparison of DCM- and CO-exposures matched for COHb revealed more pronounced performance deficit for DCM than for CO, suggesting additivity of narcotic and hypoxic action.