Forty patients undergoing gynaecological surgery were randomly assigned to receive either alfentanil and thiopentone for induction of anaesthesia, followed by alfentanil-N2O/O2 (60%/40%) for maintenance of anaesthesia, or low-dose fentanyl and thiopentone, followed by enflurane-N2O/O2 (60%/40%). More patients given enflurane developed a tachycardia (P less than 0.03) and 20% decreases in systolic and diastolic blood pressure. Times to recovery were significantly shorter after alfentanil than after enflurane. Plasma concentrations of alfentanil during induction suggested that haemodynamic and catecholamine responses were either less than, or did not differ from, baseline levels when the plasma concentration of the drug exceeded 150 ng ml-1. At extubation and the beginning of spontaneous breathing, the plasma concentration was 278 +/- 129 ng ml-1. Values for pharmacokinetic parameters of alfentanil were as follows: clearance, 5.2 +/- 2.0 ml kg-1 min-1; volume of distribution, 0.63 +/- 0.20 1 kg-1; and elimination half-life, 96.9 +/- 52.5 min. Two patients who had extended surgery had significantly lower plasma clearance of alfentanil and increased half-life. The authors conclude that the alfentanil technique was preferable to maintenance with enflurane.