Various neurophysiological properties of cannabis are described in a review of the literature. The properties of the principal active cannabinoid, delta-9-tetrahydrocannabinol (delta-9-THC) are described, followed by a review of psychological and neuropsychiatric effects. Cannabis disturbs EEG, decreasing in particular REM sleep time. Cerebral atrophy is not evident, assuming no concurrent drug abuse, but cerebral perfusion is noted to decrease after THC absorption. Endocrine effects have been described in animal studies: inhibiting effects on sex hormone production and thyroid function, and a stimulating action on corticosteroid activity have been observed. These actions are thought to exert themselves at the hypothalamic level. There is also evidence of an effect on prostaglandin metabolism. At the cellular and subcellular level THC acts on membranes of neurones and synaptic vesicles, possibly affecting membrane transport systems. The morphology of the synapse is also altered. THC acts on neurone conduction, stimulating polysynaptic transmission. Various mechanisms of THC activity are considered: via specific lipoprotein receptors, via central benzodiazepine receptors and via opioid receptors. THC also exerts an effect on neurotransmitters: an increase in central cholinergic activity, a mode-rate increase in catecholaminergic activity and effects on the GABA and serotonin systems are postulated.