In a randomly allocated double blind study of 54 primigravidae, we examined the relative efficacy of the addition of diamorphine 3 mg to either an initial bolus or an infusion of bupivacaine. Both groups received an initial bolus of 10 ml of bupivacaine 0.25% followed by an infusion of bupivacaine 0.1% at 10 ml.h-1. Group 1 received diamorphine 3 mg in the bolus and group 2 received diamorphine 3 mg in the initial 100 ml of infusion solution. Both groups had comparable total bupivacaine requirements. Analgesia, assessed by visual analogue scores, was superior at 7h in group 2, but was similar at all other times. Sedation scores were significantly lower in group 2 for the first 3h and the incidence of nausea was significantly lower in group 2. The addition of diamorphine, whether as a bolus or added to an infusion of bupivacaine, results in similar quality of analgesia, but there is a reduction in side effects when diamorphine is administered in an infusion.