Study Objective: To determine whether chronic calcium channel blocker therapy exaggerates the rise in plasma potassium concentration ([K +]) after succinylcholine administration. Design: Prospective clinical study. Setting: University and Veterans Affairs hospitals. Patients: 36 ASA physical status III and IV male patients: 21 patients taking chronic calcium channel blockers and 15 patients not receiving calcium channel blockers, all of whom were scheduled for inpatient surgical procedures with general anesthesia. Interventions: In all patients, anesthesia was induced with high-dose opioids plus a sedative-hypnotic, and intubation was facilitated with 1 to 1.5 mg/kg succinylcholine without nondepolarizing neuromuscular blocker pretreatment. Measurements and Main Results: Plasma [K +] was measured prior to induction and 1, 3, 5, 8, 11, and 15 minutes after succinylcholine was administered. A modest average peak rise of 0.5 mEq/L in plasma [K +] was observed, but there were no differences between patients who were or were not receiving calcium channel blockers. Conclusions: Patients receiving chronic calcium channel blocker therapy are at no greater risk of hyperkalemia after succinylcholine than those not taking such medications.