The value of combining morphine with bupivacaine for caudal analgesia was investigated. Thirty children, undergoing orchidopexy, received a caudal block of 0.125% bupivacaine with or without morphine 0.05 mg kg-1. Analgesia, side-effects, ventilatory frequency and oxygen saturation (SaO2) were recorded after operation. None of the 15 patients receiving the bupivacaine-morphine mixture required post-operative opioids, whereas eight of 15 patients receiving bupivacaine alone needed additional opioid analgesia. The incidence of side effects after surgery was similar for the two groups and there was no detectable difference in ventilatory frequency or SaO2.