Clostridium botulinum type A toxin-haemagglutinin complex blocks peripheral cholinergic transmission at the neuromuscular synapse by acting presynaptically at a site proximal to the site of acetylcholine release. The toxin acts on the nerve terminal by antagonizing the Ca2+-dependent events that lead to neurotransmitter release. It has no effect on postganglionic cholinergic transmission or postganglionic sympathetic transmission.