Parenteral ergometrine is widely used for the prevention and treatment of excessive uterine bleeding following birth. Unfortunately, in tropical climates it is often found to contain very little active ingredient: only 32 of 100 field samples from Bangladesh, Gambia, Malawi, Yemen and Zimbabwe contained 90-110% of the amount of active ingredient stated on the label, and 34 contained less than 60%. In this paper the results of nine studies, of which eight were initiated and coordinated by WHO, are reviewed to formulate answers to the following questions: (1) what is the extent of the problem of low potency of ergometrine in tropical climates; (2) is the problem due to instability or low initial quality, or both; (3) which practical measures can assure the quality of injectable ergometrine; and (4) are there any alternative drugs which are more stable? Injectable ergometrine is very unstable under tropical conditions and particularly if stored unrefrigerated and exposed to light, when it may loose up to 20% of its potency per month. However, there are differences between brands. Practical measures to assure the quality of injectable ergometrine therefore include a careful supplier selection and refrigerated storage. Ergometrine injection should always be protected from light until given to the patient. Loss of active ingredient can easily be detected by regular visual checks of the colour of the solution. Any discoloration implies that the solution contains less than 90% of the stated amount of active ingredient, and should not be used. Methylergometrine is no more stable than ergometrine. Parenteral oxytocin is more stable than both ergometrine and methylergometrine injection. Oral and buccal dosage forms are less stable than injections. In view of the better stability in tropical climates, similar cost, fewer side effects and comparative efficacy, parenteral oxytocin, rather than parenteral ergometrine, is the drug of choice in the prevention and treatment of postpartum haemorrhage.