The circulation of substandard medicines in the developing world is a serious clinical and public health concern. Problems include under or over concentration of ingredients, contamination, poor quality ingredients, poor stability and inadequate packaging. There are multiple causes. Drugs manufactured for export are not regulated to the same standard as those for domestic use, while regulatory agencies in the less-developed world are poorly equipped to assess and address the problem. A number of recent initiatives have been established to address the problem, most notably the WHO pre-qualification programme. However, much more action is required. Donors should encourage their partners to include more explicit quality requirements in their tender mechanisms, while purchasers should insist that producers and distributors supply drugs that comply with international quality standards. Governments in rich countries should not tolerate the export of substandard pharmaceutical products to poor countries, while developing country governments should improve their ability to detect substandard medicines.