The effects of intravenously administered lidocaine on cough suppression in elderly patients over the age of 60 yr during tracheal intubation under general anesthesia were evaluated in two studies. In the first study, 100 patients received a placebo of either 0.5, 1.0, 1.5, or 2.0 mg/kg lidocaine intravenously 1 min before tracheal intubation. All visible coughs were classified as coughing. The incidence of coughing decreased as the dose of lidocaine increased. A dose of 1.5 mg/kg or more of intravenous lidocaine suppressed the cough reflex significantly (P < 0.01). In the second study, 108 patients received 2 mg/kg lidocaine intravenously or a placebo 1, 3, 5, 7, 10, or 15 n-dn before intubation. The same criteria for determining whether a patient did or did not cough during tracheal intubation were used as in Study 1. The incidence of coughing decreased significantly (P < 0.01) when 2 mg/kg lidocaine was injected intravenously between 1 min and 3 min before attempting intubation. The cough reflex was almost entirely suppressed by plasma concentrations of lidocaine in excess of 4 mug/mL. The results suggest that intravenous administration of lidocaine is effective in suppressing the cough reflex during tracheal intubation in elderly patients under general anesthesia, but that relatively high plasma concentrations of lidocaine may be required for suppression of coughing.