The need for assessment of new medical technologies has recently become evident in many countries, especially for the people responsible for health care policy. There are multiple reasons for making evaluation: rising costs in health care, medical efficacy, safety, as well as social and political issues. Each stage of life of a diagnostic, therapeutic or preventive technology, from its emergence to obsolescence, can be assessed by an appropriate procedure. In Switzerland, a country with decentralized health care as well as political systems, the assessment is made by various institutions. Evaluative aspects are included in some National Research Foundation programs. Most work, however, is done by the division of medical techniques at the Swiss Hospital Institute. The panel of experts has recently prepared a report on magnetic resonance imaging (MRI). As a result of the initial evaluation, the need for this new technology in this country, and the number and sites of MRI systems for the next few years were established. The capital, running and unitary costs of this diagnostic procedure were estimated. The report will be of aid to the people planning investments and dealing with questions of reimbursement and other issues of health care policy. The methods of epidemiology, biostatistics, sociology and health economics used by the institutes of social and preventive medicine are very helpful in the procedures of technology assessment.