A double-blind trial has been performed to investigate the respiratory effects of low oral doses of benzoctamine, and to compare them with diazepam and a placebo. The displacement of the carbon dioxide response curves indicated that whilst diazepam caused respiratory depression, benzoctamine had a variable effect. Some volunteers showed depression, but most showed stimulation. Peak respiratory effects were seen 1 hr after oral administration, returning to normal 2-3 hr after administration. It is suggested that oral drugs given for premedication need to be administered at least 2 hr before operation to obtain maximum sedative effects at a time when respiratory effects are returning to normal. In animal experiments it has been shown that the analgesic actions of morphine are diminished by concurrent administration of benzoctamine, and that the depression of respiratory rate caused by morphine is enhanced.