Castor oil, a potent cathartic, is derived from the bean of the castor plant. Anecdotal reports, which date back to ancient Egypt have suggested the use of castor oil to stimulate labour. Castor oil has been widely used as a traditional method of initiating labour in midwifery practice. Its role in the initiation of labour is poorly understood and data examining its efficacy within a clinical trial are limited. This is one of a series of reviews of methods of cervical ripening and labour induction using standardised methodology. To determine the effects of castor oil or enemas for third trimester cervical ripening or induction of labour in comparison with other methods of cervical ripening or induction of labour. The Cochrane Pregnancy and Childbirth Group trials register, the Cochrane Controlled Trials Register and bibliographies of relevant papers. Last searched: November 2000. (1) clinical trials comparing castor oil, bath or enemas used for third trimester cervical ripening or labour induction with placebo/no treatment or other methods listed above it on a predefined list of labour induction methods; (2) random allocation to the treatment or control group; (3) adequate allocation concealment; (4) violations of allocated management not sufficient to materially affect conclusions; (5) clinically meaningful outcome measures reported; (6) data available for analysis according to the random allocation; (7) missing data insufficient to materially affect the conclusions. A strategy has been developed to deal with the large volume and complexity of trial data relating to labour induction. This involves a two-stage method of data extraction. In the one included study of 100 women, which compared a single dose of castor oil versus no treatment, no difference was found between caesarean section rates (relative risk (RR) 2.31, 95% CI 0.77, 6.87). No data were presented on neonatal or maternal mortality or morbidity. There was no difference between either the rate of meconium stained liquor (RR 0.77, 95% CI 0.25,2.36) or Apgar score < 7 at 5 minutes (RR 0.92, 95% CI 0.02,45.71) between the two groups. The number of participants was small hence only large differences in outcomes could have been detected. All women who ingested castor oil felt nauseous. The only trial included in this review attempts to address the role of castor oil as an induction agent. The trial was small and of poor methodological quality. Further research is needed to attempt to quantify the efficacy of castor oil as an induction agent.