A brief account is given of the pharmacological properties of a new intravenous anaesthetic, G.29.505. In three series of 200 patients undergoing dental extractions, anaesthesia was induced respectively with G.29.505, thiopentone, and methohexitone, and maintained with nitrous oxide and oxygen. The time taken to settle the patient, the character of anaesthesia and recovery were noted, and the speed of recovery of consciousness and ambulation were recorded. It was found that G.29.505 had demonstrable advantages over thiopentone and methohexitone but it caused an unduly high incidence of venous thrombosis. Until the drug can be rendered non-irritant, methohexitone is considered the agent of choice for intravenous induction of anaesthesia for brief surgical procedures.