It is common practice at the Hospital for Sick Children, Toronto, to administer atropine 20 mu g.kg(-1) prior to succinylcholine in infants and children. It is unclear whether ''prophylactic '' administration of this dose of atropine to older children (6-16 yr) ir necessary. This study war designed to compare the changes in heart rate, rhythm and mean arterial pressure after administration of either atropine 10 or 20 mu g.kg(-1) with succinylcholine or vecuronium (control group) to older children anaesthetized with thiopentone. Thirty-six ASA I or II patients (6-16 yr) were studied Anaesthesia was induced with thiopentone 5 mg.kg(-1). Patients were randomly assigned to receive: (a) atropine 10 mu g.kg(-1) and succinylcholine 1.5 mg.kg(-1) (n = 12), (b) atropine 20 mu g.kg(-1) and succinylcholine 1.5 mg.kg(-1) (n = 13) or (c) vecuronium 0.1 mg.kg(-1) (n = 11) to facilitate tracheal intubation. Heart rate and rhythm were recorded continuously using a computerised analogue interface whereas blood pressure was monitored non-invasively before induction of anaesthesia, immediately before and at one and three minutes after laryngoscopy. No difference was observed between patients who received atropine 10 or 20 mu g.kg(-1) prior to succinylcholine. No episode of sinus bradycardia occurred. Premature atrial contractions were observed in two patients (one succinycholine/atropine 20 mu g.kg(-1), one vecuronium). Administration of atropine 20 mu g.kg(-1) prior to succinylcholine provides no advantage over atropine 10 mu g.kg(-1) in older children in terms of cardiovascular stability.It is common practice at the Hospital for Sick Children, Toronto, to administer atropine 20 mu g.kg(-1) prior to succinylcholine in infants and children. It is unclear whether ''prophylactic '' administration of this dose of atropine to older children (6-16 yr) ir necessary. This study war designed to compare the changes in heart rate, rhythm and mean arterial pressure after administration of either atropine 10 or 20 mu g.kg(-1) with succinylcholine or vecuronium (control group) to older children anaesthetized with thiopentone. Thirty-six ASA I or II patients (6-16 yr) were studied Anaesthesia was induced with thiopentone 5 mg.kg(-1). Patients were randomly assigned to receive: (a) atropine 10 mu g.kg(-1) and succinylcholine 1.5 mg.kg(-1) (n = 12), (b) atropine 20 mu g.kg(-1) and succinylcholine 1.5 mg.kg(-1) (n = 13) or (c) vecuronium 0.1 mg.kg(-1) (n = 11) to facilitate tracheal intubation. Heart rate and rhythm were recorded continuously using a computerised analogue interface whereas blood pressure was monitored non-invasively before induction of anaesthesia, immediately before and at one and three minutes after laryngoscopy. No difference was observed between patients who received atropine 10 or 20 mu g.kg(-1) prior to succinylcholine. No episode of sinus bradycardia occurred. Premature atrial contractions were observed in two patients (one succinycholine/atropine 20 mu g.kg(-1), one vecuronium). Administration of atropine 20 mu g.kg(-1) prior to succinylcholine provides no advantage over atropine 10 mu g.kg(-1) in older children in terms of cardiovascular stability.