Since 1980, many of the state governments in India have introduced programmes to integrate traditional medical systems (TM) into official health care institutions and services at different administrative levels. One of these schemes is at Primary Health Centres (phcs) in various districts. However, little research has been undertaken to date on relative demand and utilization, or on the extent to which TM is seen or used as a complement, alternative or supplement to biomedical services, in the same phc setting. The consumer assumes an important role in an integrated approach, where illness behaviour is understood to be a decision-making process. From the structuralist aspect also, the needs and decisions (in a given situation) as perceived by the administration are not necessarily the same as subjectively felt needs, wants, or even expressed needs of individuals. It is hoped research into the degree of usage and levels of clinical utilization of the two coexisting services will be useful in planning norms and services, estimation of recurrent expenditures and allocation of resources for effective functioning of the phcs. This paper presents the findings of a questionnaire based on a quota sample of users of phcs. eighty patients in each of the Allopathy and Siddha medicine wings were interviewed in three phcs in Tamil Nadu, a total of 480 respondents. The main issues considered in this paper are: 1. Socio-economic characteristics of the users. 2. Treatment patterns: differential preferences for treatment methods for various disease conditions; multiple-usage - interchangeable or concurrently for the same ailment; degree of medical pluralism; spatial patterns of movement. 3. The reasons for participating in the present treatment. 4. Behaviour, satisfaction, attitudes, opinions, preferences, experiences. 5. Conclusions and implications of the study for research and service planning. This study, although based on small and not necessarily representative samples, illustrates some of the potentials and shortcomings of an integrated approach at the institutional level.