In this study the effect of general anaesthesia on the success of embryo transfer was investigated. Between January and August 1986, in a preliminary trial using general anaesthesia for embryo replacement (sodium thiopentone and alfentanyl), the overall pregnancy rate was 36% (n = 86), compared to 21% in a group of matched controls without anaesthesia (n = 131). Following the preliminary study in a larger series of patients between August 1986 and December 1987, all embryo transfers were performed using general anaesthesia. In a total of 795 embryo replacements the pregnancy rate was 19%. This was neither significantly different from the overall pregnancy rate of the non-anaesthetic controls of the preliminary study (21%), nor from a group of 603 patients who received embryo replacement without anaesthesia between June 1984 and December 1985. The results of this study indicate no obviously adverse effect of the anaesthesia on the induction of pregnancy. The results of the preliminary study even indicate a beneficial effect of anaesthesia on the pregnancy rate. However, to assess accurately the effect of general anaesthesia, a large prospective randomized study is needed. The type of anaesthesia used in this study, however, may be useful in cases of difficult transfer procedures, due to psychological stress to the patient, or technical/mechanical problems during the embryo transfer procedure.