Institutional innovations are increasingly seen as key to achieving not only agricultural growth, by overcoming market failures, but also to ensure that poor smallholders also benefit from this process. This paper analyses institutional arrangements for vegetable marketing in East Africa from a transaction cost perspective. Marketing of vegetables is still dominated by spot markets with some, but still limited, movement towards farmers' engaging collectively in contract farming through producers' organisations. It appears that little is understood concerning how farmers and traders have overcome transaction costs in such situations, and this area deserves increased attention. An understanding of how institutional change occurs is necessary if donor agencies wish to support this process.