Mivacurium is a potent, short-acting, nondepolarizing relaxant of the benzylisoquinoline series. In adults endotracheal intubation can be performed after a 2 x ED95 dose of 0.15-0.2 mg/kg within 2-2.5 minutes. In infants onset time and clinical duration of mivacurium are significantly shorter than in adults. Although the onset time of mivacurium is similar to that of other relaxants like vecuronium and atracurium, its clinical duration is unique in comparison with all other nondepolarizing relaxants currently available. Mivacurium shows no cumulative effect either after repeated injections or after continuous infusion. In contrast to other relaxants, an increasing dose of mivacurium leads only to a slight increase in clinical duration and has no effect on the recovery index. After spontaneous recovery has reached 10-25% of the control value, the neuromuscular block can be easily antagonized with neostigmine or edrophonium. The properties of mivacurium described above are related to patients with normal pseudocholinesterase activity. Particularly patients with atypical pseudocholinesterase show a marked increase in clinical duration. Side-effects due to significant histamine release with flush, tachycardia and hypotension are seldom observed if mivacurium is injected slowly over a period of more than 30 seconds and bolus injections of more than 2 x ED95 or 3 x ED95 are avoided.