One hundred unpremedicated patients, undergoing short gynaecological procedures, were randomly allocated to receive one of three i.v. hypnotic agents (methohexitone, Althesin and etomidate) alone or in combination with fentanyl, to supplement 66% nitrous oxide in oxygen. Recovery was assessed by the time patients took to open the eyes, to give correct date of birth, to achieve a certain level of manipulative skill with a children's post-box toy, and to perform a paper and pencil test. Satisfactory operating conditions were not obtained using etomidate alone. Administration of methohexitone alone resulted in a more rapid initial awakening than Althesin alone (P less than 0.05) and the administration of fentanyl with methohexitone reduced the total dose given of the latter (P less than 0.01). Administration of fentanyl with Althesin or methohexitone did not significantly prolong the "post-box" recovery time. Side-effects were less common with Althesin, with or without fentanyl and etomidate with fentanyl was associated with the greatest frequency of complications.