Twelve patients with mechanical infertility in the in vitro fertilization program were studied. Seven of them received halothane anaesthesia and the other five received neuroleptanaesthesia. Higher plasma prolactin levels and lower plasma progesterone levels were observed in the neuroleptanaesthesia group than in the halothane group during and after transvaginal ultrasound-guided oocyte pick-up. Plasma adrenocorticotropic hormone and cortisol levels of the patients suggested that surgical stress was minimal in both groups. It is likely that droperidol and fentanyl, both used in neuroleptanaesthesia, were responsible for the hyperprolactinaemia which was followed by inhibition of progesterone production. These agents, therefore, are not recommended as anaesthetic agents for transvaginal ultrasound-guided oocyte pick-up.