In a randomised controlled trial of mothers in labour intramuscular pethidine 150 mg, repeated if necessary, was compared with self-administered intravenous pethidine (0.25 mg/kg available at 10-min-intervals). Each mother agreed to have either method of pain relief and could opt for epidural block. The intramuscular group had significantly more pethidine than the intravenous group (mean differences, primipara 29 mg; multipara 16 mg). Ratings by mothers of the pain of 1st, 2nd stage and overall (analogue scores and gradings) were consistently better for the intravenous group although not significantly different. There were no differences in mean Apgar scores between the babies in the groups. In mothers who do not choose epidural block, similar pain relief is afforded by adequate intramuscular pethidine or self-demand intravenous pethidine; however, intravenous self-administration is more efficient since the pain relief is achieved with a lower dose of pethidine.