Physostigmine was administered intravenously to 25 patients, anaesthetised with sodium gamma-hydroxybutyrate (GHB), and their emergence from anesthesia was studied. Physostigmine (2 mg) brought about rapid, safe, reliable and sustained awakening after a "latent period" varying from 2-10 minutes (mean 6-2 minutes+/-S.D. 2-2) in 24 patients. In the one patient not awake at 10 minutes, a second dose of physostigmine produced awakening in an additional 8 minutes. No serious side effects were attributable to the physostigmine. This finding may warrant a reconsideration of the place of GHB in anaesthetic practice.