The venom of the common Indian catfish P. canius Hamilton (locally called 'Kanmagur') was examined for its pharmacodynamic activity. The LD50 of the venom in mice was found to be 3.9 mg/kg (ip). At lower doses, the venom produced a positive inotropic effect on toad and rabbit hearts, while at higher doses it produced cardiac arrest. In the isolated guineapig auricle, the venom increased the rate and amplitude of contraction. The venom increased rat blood pressure - an action antagonised by α-adrenergic blocker (phenoxybenzamine). It reduced the rate and amplitude of rat and guineapig respiration leading to respiratory arrest and death. The venom did not alter the cutaneous capillary permeability of guineapig but produced vasoconstrictor effect on rat hindquarter perfusion. It induced contractions in several smooth muscle preparations viz., ileum and colon of guineapig, fundus, uterus and ileum of rat. On isolated guineapig ileum, the venom produced contraction which was not antagonised by atropine and mepyramine, but was partially antagonised by methysergide associated with a residual contraction which was abolished by SC 19220, a prostaglandin receptor blocker. The venom produced irreversible blockade of electrically induced twitch response on isolated rat phrenic nerve diaphragm and chick biventer cervicis preparation. Haemolysis was not produced by the venom on mice, guineapig and human RBC (washed).