Abstract: Experiments were carried out on isolated rat phrenic nerve diaphragm preparations and Chick biventer cervicis preparations. Dimethyltrilobine iodide (DTI) blocked neuro-muscular transmission without affecting the conductivity of the nerve and muscle contractile response to direct stimulus. The actions of DTI was compared with those of curare in vitro. The ID₅₀ of DTI and curare were found to be 1.9 × 10^-5M and 8.0×10^-7M respectively, DTI reduced the sensitiyity of the chick biventer cervicis muscle to Ach. High Ca²⁺ antagonised the effect of DTI on neuro-muscular transmission. It is concluded that DTI produces a neuromuscular block by acting on the Ach receptor.