A prospective randomized study of 296 patients was undertaken to evaluate the efficiency of 15 mg prostaglandin F2 alpha (PGF2 alpha) suspended in tylose gel and applied intracervically for labour induction. The control group was treated with standard oxytocin intravenous infusion. Results indicated that local PGF2 alpha was superior to oxytocin therapy in shortening the duration of labour (6.3 +/- 2.3 versus 8.1 +/- 2.6 hours, p < 0.05). Only 19% of the patients treated with PGF2 alpha required oxytocin augmentation during labour. Our data suggest that PGF2 alpha treatment is associated with few maternal side-effects, few failed inductions, a low operative delivery rate and favourable neonatal outcome. To investigate the influence of PGF2 alpha for labour promotion we have measured interstitial collagenase and elastase activity in the lower uterine segment after both methods of labour induction. The total collagenase activity was 22 times higher in tissue samples obtained from patients in active spontaneous and oxytocin-induced labour, compared with women not in labour (at term) (p < 0.001). The total interstitial elastase activity was 2-fold higher in women in active labour than in patients at term (p < 0.03). A significantly higher collagenase and elastase activity was observed in uterine specimens obtained from patients treated with PGF2 alpha compared to oxytocin, and this indicates that cervical collagen may be digested more quickly in the presence of exogenous prostaglandin F2 alpha.