Uterine activity was studied in 35 nulliparous Thai women who were in the active phase of spontaneous labour, and who were delivered vaginally without supplementary oxytocin or assisted delivery. A catheter-tip pressure transducer coupled with a uterine activity integrator was used to measure and quantitate uterine activity. Progression of normal labour was defined as labour progressing along the Friedman's curve in the active phase. In nulliparous Thai women, the minimum level of uterine activity likely to be associated with labour progress was 322 kPas/15 min at 3 cm cervical dilatation. The mean and median levels in the active phase of normal labour were 1,075.6 and 952.0 kPas/15 min, respectively. There was a weak correlation (R = 0.3) between an increasing cervical dilatation and uterine activity.