In vitro toxicological evaluation of Nerium oleander was carried out u
sing different isolated preparations. The methanolic leaf extract pote
ntiated both spontaneous and electrically evoked contractions of vas d
eferens of rats and guinea-pig ileum in a concentration dependent mann
er. The effect was not antagonized by the adrenergic blocker, tolazoli
ne. The extract inhibited electrically stimulated neurogenic twitch re
sponses of rat phrenic nerve diaphragm preparation. The dose dependent
inhibition of twitch response in this preparation could not be revers
ed by the anticholinesterase drug, neostigmine. The extract evoked a p
ersistent depolarizing effect on the phrenic nerve diaphragm preparati
on. The extract exhibited its most potent action on the isolated right
atrial preparation of rat. It inhibited the rate of spontaneously bea
ting atria in a concentration dependent manner. The negative chronotro
pic effect was not antagonized either by antimuscarinic drug or adrene
rgic agonist.