Cis-atracurium is a stereoisomer of atracurium, about five times more potent than the racemate. Whereas cis-atracurium is routinely used in adults, its effects on children are still poorly defined. We compared equipotent doses of atracurium and cis-atracurium in children aged between 2 and 12 years regarding the quality of neuromuscular blockade, the intubation conditions and the occurrence of side-effects. After approval by the ethics committee and with informed parental consent, 84 children (ASA I or ASA II) were randomly allocated to receive either 0.5 mg/kg atracurium (group A, n = 42) or 0.1 mg/kg cis-atracurium (group C, n = 42). In both groups anaesthesia was induced with 15 micrograms/kg alfentanil and 5-7 mg/kg thiopentone. We assessed the intubation conditions according to the Krieg Scale. Anaesthesia was maintained with a nitrous oxide/oxygen mixture of 2:1 and isoflurane in an endexpiratory concentration of approximately 0.6 Vol.%. Neuromuscular blockade was controlled acceleromyographically in response to supramaximal stimulation of the ulnar nerve. We measured the onset time (T1 = 5%), duration of effect (T1 = 25%), recovery index (T1 = 25%-75%) and the recovery time at a train-of-four-ratio (T4/T1) of 0.7. These parameters did not show any significant differences between group A and group C: onset time: 3.1 +/- 1.5 min (group A) versus 3.4 +/- 1.1 min (group C), duration of effect: 34.1 +/- 5.5 min (group A) versus 34.1 +/- 6.5 min (group C), recovery index: 9.3 +/- 3.3 min (group A) versus 9.6 +/- 2.5 min (group C), recovery time at a TOF-ratio of 0.7:49.3 +/- 8.4 min (group A) versus 52.3 +/- 6.6 min (group C). In group A, the intubation conditions were "excellent" or "good" in 98% of the patients, whereas in group C the figure was only 69%. Regarding side-effects, we found significantly more frequent urticaria in group A (6 of the 42 patients) (p < or = 0.05) than in group C, in which no patient showed urticaria. Flush and tachycardia occurred much less frequently and there were no significant differences in the two groups: two patients in group A and only one in group C. The authors conclude that atracurium and cis-atracurium lead to comparable neuromuscular effects in children aged between 2 and 12 years. Only the intubation conditions were better after atracurium, but atracurium was followed by urticaria more often than cis-atracurium.