1 Two antitussive agents (+/-)-glaucine phosphate and codeine phosphate have been compared with placebo with respect to ventilation, ventilatory response to carbon dioxide, pulse, blood pressure, digit symbol substitution, sedation score and the Zahlen-Verbindung test performance in ten healthy volunteers (22-36 years). The study was double-blind and the two doses of each antitussive agent and the placebo were administered as a syrup. 2 Both codeine phosphate and (+/-)-glaucine phosphate displaced the ventilatory response to carbon dioxide to the right. 3 The effect of codeine phosphate on the ventilatory response to carbon dioxide was not dose dependent: 30 mg produced greater effects than the 60 mg dose. 4 Only the highest dose of (+/-)-glaucine phosphate (60 mg) caused respiratory depression and this was associated with sedation and decreased performance in the digit symbol substitution test. 5 Neither antitussive agent had significant effects upon pulse or blood pressure and codeine phosphate had no detectable sedative activity.