The objective of this study was to evaluate onset times and tracheal intubating conditions after administration of rocuronium or mivacurium in children of different ages. In this randomized double-blind study, 40 healthy (ASA I) children aged 1 to 14 years were studied. They were divided, according to age, into two groups: Group A (n=20) included patients 1 to 3 years of age and Group B (n=20) 4 to 14 years of age. After general anesthesia induction patients in both groups were further divided into two subgroups. So, half of patients (n=10) of each group were randomly assigned to receive a bolus of either rocuronium 0.6 mg*Kg-1 or mivacurium 0.2 mg*Kg-1. The onset time of neuromuscular blockade (from 100% to 0% response) was assessed by the accelerographic response (100-0%) of the adductor pollicis, stimulating the ulnar nerve with single twitch stimuli. Tracheal intubating conditions were assessed as good, excellent or poor, 60 sec after the initial dose of relaxant by an anaesthetist who was unaware of patient group. Statistical analysis was performed with Student t-test or Fisher’s exact test, where appropriate. Statistical significance was assumed at the level of p<0.05. Demographic data were similar between subgroups of each range of age. Intubating conditions did not differ significantly between groups although the incidence of excellent grade intubations was higher with rocuronium. The onset time of neuromuscular blockade was found significantly shorter in the subgroup of rocuronium compared with mivacurium, while for the same drug regimen no significant difference was found between groups A and B. This study demonstrates that, regardless children΄s age, the onset time of rocuronium is shorter than mivacurium, while both drugs provide within 60 sec excellent intubating conditions in the majority of cases.