Informal savings and borrowing institutions are a way to intermediate between savers and borrowers in the developing world. But if these associations attract mostly savers or mostly borrowers, or are concentrated in one occupation, they may not function as well as they should. This column uses survey results from Malawi to suggest that commitment savers and borrowers mix in such associations, but occupations have tended to stick together. This may make them vulnerable to shocks such as a bad harvest.