This paper focuses on the environmental knowledge of farming communities in Africa. How can the researcher investigate such knowledge? How can it be used in the rural development process? The scope and limitations of farmers' knowledge concerning agricultural pests is illustrated in a case study. The process of knowledge formation is a consequence of the kinds of observation the farmer is able to make. Inaccuracies may stem from observational limitations. On the other hand the farmer's own point of view reflects dimensions of experience of which the researcher or extension agent may be unaware. These dimensions may be vital to the success or failure of rural development schemes and should be systematically incorporated into the ‘research and development’ process. This in itself implies new approaches to eliciting information which hand over the initiative in interviews to the respondent. Repertory grid analysis is discussed as an example of a relevant methodology. The paper finally discusses how an improved capacity to research and monitor development problems at the village level might help redress the imbalance which results from technocratic control of planning decision making.