This study was designed to measure how fast and at what concentrations ketamine would enter the foeto-placental circulation, when administered intravenously to 10 healthy mothers immediately before forceps delivery, which was indicated by a delayed second stage of labour. It is shown that ketamine very rapidly passes the placenta, and that ketamine levels in cord blood exceed the levels in the maternal venous blood as early as 1 min 37 s after the injection. The ketamine levels in cord blood reach a maximum in the period 1 min 37 s to 2 min 5 s after the injection. Later they show a tendency to decline. A short-lasting, marked elevation of blood pressure was produced by the ketamine anaesthesia. Two of the newborn showed low Apgar scores at 1 min. In one of them this was probably attributable to the anaesthesia.