The classification of neuromuscular diseases with regard to the use of muscle relaxants is based on the localisation of the particular abnormality. Three types of syndromes can be differentiated: (1) denervation states; (2) disturbances of neuromuscular transmission; and (3) intracellular disease. Succinylcholine should be avoided in all types of denervation syndrome due to the possibility of life-threatening hyperkalaemia. The time frame during which succinylcholine must be avoided following a traumatic denervation or burn begins 24 h after the event. The exact period of risk is unknown, but a duration of 6 months can be considered the absolute minimum. Patients may display increased sensitivity to non-depolarising muscle relaxants following damage to the second motoneuron (e.g., amyotrophic lateral sclerosis), whereas in diseases of the first motoneuron (e.g., cerebral apoplexy), increased resistance to muscle relaxants may be observed in the affected parts of the body. In diseases of the neuromuscular junction (myasthenia gravis) there is increased sensitivity to non-depolarising muscle relaxants. No complications have been described following the use of succinylcholine in these patients, however, the use of reversal agents may lead to prolongation of the effect of succinylcholine. Patients with a primary myopathy may display increased sensitivity to non-depolarising muscle relaxants. The use of drugs with acetylcholine-like actions (succinylcholine, reversal agents) should be avoided due to the danger of triggering muscle spasms in patients with myotonic disease and the risk of rhabdomyolysis in patients with dystrophic muscle disease. Irrespective of the type of muscle disease present, titration of the dose of muscle relaxant should always be done using a nerve stimulator.(ABSTRACT TRUNCATED AT 250 WORDS)