8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazol[1,5-a][1,4]benzodiazepine (midazolam maleate, Ro 21-3981, Dormicum) or thiopental were administered to 99 women undergoing short gynecological surgical procedures for induction and maintenance of anesthesia along with 67% nitrous oxide. Either fentanyl 1.5 microgram kg-1 or a saline placebo were given i.v. as acute premedication 5 min before induction. We measured the quality of induction and maintenance. Induction was more rapid after thiopental but thiopental produced more apnea especially when combined with fentanyl. Fentanyl premedication reduced the dose of hypnotics necessary to keep patients asleep. It was difficult to keep patients from moving during the procedure when only the hypnotics and nitrous oxide were used, so the use of these drugs for both induction and maintenance is recommended only when combined with narcotics or other analgesics. Although recovery after midazolam was slower than after thiopental, it was without untoward reactions such as hallucinations or excitement. Vomiting was less frequent after midazolam. Midazolam produced a profound period of amnesia for 1-2 h, so important instructions could not be given to patients during this time. All patients were awake enough to discharge from the hospital 200 min after the last dose of hypnotic was given. We would recommend a combination of midazolam, fentanyl and nitrous oxide for induction and maintenance of anesthesia for short surgical procedures except when a rapid induction is desired, then thiopental is preferred as the hypnotic.