This proposal incorporates three foci that elaborate the behavioral high-risk paradigm as applied to affective disorders. The first concerns further refinement of the item set and case-identification properties of an inventory which is used to identify cyclothymic individuals who are at risk for developing full syndromal bipolar affective disorder. These aspects of the inventory are evaluated in a major interview validation study, the goal of which is to define a highly stable inventory so that other investigators may use it. The second focus involved the extension of the behavioral high-risk paradigm to the identification of certain forms of dysthymia which have been related to cyclothymia via a multiple-threshold model of inheritance. These studies include two independent validations of new Dysthymic Inventory developed by the PI. The goal of these studies is to provide a stable inventory that will allow comparitive research on cyclothymia and dysthymia. The third focus of the proposal concerns the application of the behavioral high-risk paradigm in a manner for which it was developed: to assess the psychobiologic factors in subsyndromal affective disorders which may serve as predictors of future clinical outcome. In this case, circadian rhythm functioning in cyclothymia, and later in the period dysthymia, is proposed. Several rhythms of subjects are monitored continuously for approximately 60 days while they live in their natural environment under changing conditions of life stress. It is through the latter type of work, in particular, that predispositional nature of bipolar disorder may be investigated. Without an adequate high-risk paradigm, predispositional variables will not be accessible to investigation. The behavioral high-risk paradigm provides one promising means to this end.