4-aminopyridine is the first of the aminopyridines to be used in clinical practice. It blocks potassium channels and thereby increases acetylcholine, and possibly noradrenaline, release at nerve terminals. In man the drug has a significant action at the neuromuscular junction, but has little effect on the autonomic nervous system or muscle (smooth, skeletal, or cardiac) although such actions have been demonstrated in animals. It may be clinically useful in the reversal of nondepolariser blockade and a role in antibiotic associated block has been proposed. It may be used effectively as an analeptic agent. It appears to be a useful therapeutic agent in myasthenia gravis and Eaton Lambert syndrome, although of limited use in botulism. It effects on the central nervous system are considerable. These account for the major side effects of the drug which include tremor, excitability and convulsions.