An ethanol extract of the leaves of Ocimum sanctum was screened for its effects on the central nervous system. It prolonged the time of lost reflex in mice due to pentobarbital, decreased the recovery time and severity of electroshock- and pentylenetetrazole-induced convulsions, and decreased apomorphine-induced fighting time and ambulation in "open field" studies. Using a behavioural despair model involving forced swimming in rats and mice, the extract lowered immobility in a manner comparable to imipramine. This action was blocked by haloperidol and sulpiride, indicating a possible action involving dopaminergic neurones. In similar studies, there was a synergistic action when the extract was combined with bromocriptine, a potent D2-receptor agonist.