It is now widely accepted that technological change is a necessary although by no means sufficient condition for agricultural development. It is clear that despite the widespread diffusion of new wheat and rice varieties, many new technologies are not being widely used by farmers because they do not fit the particular circumstances of farmers for whom they are intended. This is despite the fact that considerable public expenditures are often made to provide the infrastructure such as credit and markets to enable the farmer to adopt these tee hnologies. This paper attempts to synthesize our experiences with national research programmes and with the International Wheat and Maize Improvement Center's (CIMMYT) wheat and maize programmes in deveolping research methodologies to ensure that agricultural technologies generated by scarce research resources are consistent with the circumstances of target farmers. It emphasizes collaboration of technical and social scientists in on-farm research--both in diagnosing farmers' problems and demands for technology and in developing and testing in farmers' fields those technologies which appear to meet these problems.