A missing link in knowledge about health care utilization is the effect of differing affiliations of patients with providers of medical care: what provider is selected for what service, how providers are selected, what degree of continuity in use of providers is manifest, etc. The concept of affiliation is developed in terms of seven "parameters": identity, setting, structural dominance, specificity/generality, external constraints, history and salience. This conceptual structure forms the basis for the development of a set of hypotheses which test the more general proposition that, other things being equal, the nature of provider-patient affiliations is a determinant of the extent of use of health services. Data on these matters is to be gathered through the survey method. An interview survey of a sample of some 3000 households in Rhode Island will form the basic data source for the project. This will be supplemented by a counter-seasonal follow-up sub-sample. It is also proposed to study the factors involved in the development of patient-provider affiliations. In order to accomplish this, interviews will be held about six months after their arrival in Rhode Island of a group of migrants to the state. Attention will be paid to how they select health care practitioners and settings -- if, indeed, they have done so within this time period. Ways in which migrants develop affiliations in other institutional contexts will also be studied.