Farming systems research has set itself the ambitious goal of developing technologies that are widely adopted by resource poor farmers. This goal has generally proved to be far more elusive than originally hoped. The problem does not lie with the principles of farming systems research (i.e., research that is farmer oriented, interdisiciplinary and employs a systems perspective). Part of the problem, particularly for Sahelian countries, is the lack of technologies "on the shelf" to offer farmers. Part of the problem, also,is inadequately developed markets for credit, inputs and products. Even when due allowance has been made for these constraints, however, farming systems research has not yielded its full potential. The reason is simple - farming systems research is hard to do (Herdt, 1987). It is physically hard, and it is intellectually hard. Conventional research tools are not well adapted to farmer participatory research. Communication, with farmers and with other disciplines, is a struggle. As a result, every farming systems research team (and every team member) must engage in a learning process through which the necessary expertise and mutual understanding can be developed. The goal of this paper is to make a contribution to this learning process, in the Senegalese context. The subject matter is the economic analysis of on-farm trials. What can be learned from such analysis that is useful to farming systems or commodity-oriented research teams? How should it be done and what practical advances in method have taken place recently? What data are required and how should they be collected? Although the subject matter is economic analysis, the paper is addressed to team members from all disciplines. Like new technology, the information gained from economic analysis is only useful if it is adopted, i.e., incorporated into the design of further experimental work or the formulation of farmer recommendations. This can only be achieved if the objectives, concepts and methods of economic analysis are understood and accepted by all team members.