Relationships between medical services research and health policy are examined in the light of a study evaluating a major health policy measure in Finland, the national health insurance scheme introduced in 1964. A nationwide health interview survey was made immediately prior to introduction of the scheme and again four years later. The results show that the ratio between care obtained and care needed had become more uniform among various population groups after the inception of national health insurance than previously. Only a small increase was found in the overall utilization rates of most types of health services. Also, the number of restricted activity days did not increase with the introduction of daily sickness allowances. In spite of minor deficiencies, the changes caused by the implementation of the national health insurance seem to have been in accordance with its main objectives. However, the results suggest that financial arrangements, i.e., health insurance, must be accompanied by other measures (in Finland an increase in the supply of ambulatory health services) if the objectives of health policy are to be obtained on a more satisfactory scale. The applicability of this evaluation study to the planning of other health activities is also discussed.