The neuromuscular and cardiovascular effects of doxacurium chloride (BW A938U) were evaluated in 27 children (2-12 yr) anaesthetized with 1% halothane and nitrous oxide in oxygen. In nine children the incremental technique was used to establish a cumulative dose-response curve by train-of-four stimulation. The remaining children received either 30 or 50 micrograms kg-1 of the drug as a single bolus. The median ED50 and ED95 of doxacurium in children were 19 and 32 micrograms kg-1, respectively. No clinically significant change in heart rate or arterial pressure occurred. Following doxacurium 30 micrograms kg-1 and 50 micrograms kg-1, recovery to 25% of control occurred in 25 (SEM 6) and 44 (3) min, respectively. The recovery index (25-75% of control) was 27 (2) min. The duration of action of doxacurium is similar to that of tubocurarine and dimethyl-tubocurarine in children. Compared with adults, children seem to require more doxacurium (microgram kg-1) to achieve a comparable degree of neuromuscular depression, and they recover more rapidly.