Fetal bradycardia due to uterine hypertonia was observed after the intravenous administration of pethidine (meperidine) 75 mg with promethazine 25 mg during active labour. These analgesic drugs are known to affect uterine contractions by enhancing both amplitude and frequency, but are thought to affect uterine tone minimally. Twenty cases of uterine hypertonia resulting in fetal bradycardia were monitored in a period of 6 months in women receiving these drugs during labour. In all cases, the uterine hypertonia appeared shortly after the drug administration. The uterine hypertonus as well as the fetal bradycardia were self limited and no intervention was undertaken. Recognition of this phenomenon is important in order to prevent unnecessary anxiety on the part of medical attendants.