The dose-response relationship, onset, duration of action, atropine requirement, and pharmacokinetic variables of edrophonium were determined in infants and children during N2O–halothane anesthesia. The technique of steady state infusion ofd-tubucurarine (dTc) was used to determine the ED50for edrophonium (i.e., the dose producing 50% antagonism of 90% neuromuscular depression) in 14 infants (145 μg/kg) and 12 children (233 μg/kg). The reported values for ED50for edrophonium (obtained under similar anesthetic conditions) is 128 μg/kg for adults. These three dose–response curves do not differ statistically; however, there was greater variability among infants and children than adults. Time to peak antagonism was similar for all three age groups. Duration of antagonism was determined in six infants and six children and did not differ from the reported value for adults. The optimal dose and time of administration of atropine were established by administering edrophonium (1 mg/kg) and atropine (10–20 μg/kg) to 24 infants and children. The smallest changes in heart rate and systolic blood pressure occurred when atropine (10 μg/kg) was givne 30 s before edrophonium. The pharmacokinetics of edrophonium (1 mg/kg) were studied in four infants and four children and were compared with published values for adults: distribution and elimination half-lives and distribution volumes were similar for the three groups. Total clearance (ml · kg-1· min-1) was greatest for infants (17.8 ± 1.2) compared with children (14.2 ± 7.3) and adults (8.3 ± 2.9). The authors conclude that the dose of edrophonium required to antagonize dTc-induced neuromuscular blockade is similar or possibly greater for infants and children than for adults. Onset and duration of antagonism are similar for all three age groups, despite age-related differences in total clearance. Edrophonium, 1 mg/kg, appears to antagonize neuromuscular blockade effectively in infants and children; cardiovascular changes can be minimized by administering atropine (10 μg/kg) 30 s before edrophonium.