Postpartum haemorrhage (PPH) causes preventable maternal deaths, mainly in low-income countries. Misoprostol has powerful uterotonic effects and, because it is well absorbed orally and sublingually, has the potential to be used more widely than would be possible with injectable uterotonics alone. Misoprostol is clearly less effective than oxytocin. Placebo-controlled studies have had variable results, although two recent trials in low-income communities have shown promising results. The main recognized side effects have been dose-related pyrexia and shivering, including occasional hyperpyrexia. In the randomized trials reported to date, there has been a trend to more deaths with misoprostol than with the control groups. The dose that has been most commonly used in clinical trials for preventing PPH is 600 microg orally. Meta-analysis of direct and adjusted indirect comparisons between 600 and 400 microg showed very similar effectiveness. To date, there is very limited evidence for the effectiveness of misoprostol, the lowest effective dose and the magnitude of adverse effects, both direct and indirect. The need for further research is a matter of great urgency.