One hundred female patients were allocated randomly to receive either no analgesic supplementation to methohexitone, nitrous oxide in oxygen anaesthesia, or supplements of fentanyl 1.5 micrograms kg-1 or alfentanil 8, 12 or 16 micrograms kg-1. No differences were seen in the time to recover consciousness, regain orientation or manipulate shapes into a box. Analgesic supplementation resulted in a decrease in the requirement for methohexitone, and improved operating conditions. Some patients in each group who received fentanyl or alfentanil became apnoeic for more than 30 s duration. The duration of apnoea increased with larger doses of alfentanil.