The analgesic efficacy and safety of tramadol 50 mg, 100 mg and pethidine 75 mg, administered intramuscularly were compared in a randomized, double-blind clinical trial in 90 pregnant women with labour pain. Pain relief was measured by a 4-point verbal rating scale 10, 20, 30, 45 and 60 min after the administration of study drugs. The average total pain relief score within the first hour was 0.9 with tramadol 50 mg, 1.7 with tramadol 100 mg and 1.7 with pethidine 75 mg. In comparison to both tramadol doses the administration of pethidine was associated with a significantly higher frequency of adverse events and a significantly lower respiratory rate in the neonates. The results indicate that tramadol 100 mg is as effective as pethidine 75 mg but has a superior safety profile.