This study was undertaken to determine the comparative validity of two competing hypotheses derived from different conceptualizations of internal versus external control. On the basis of the premise that this dimension is merely a belief on the periphery of personality, it was predicted that headache patients who felt that they could exert some influence over their own health would become more involved in and hence derive more benefit from both psychotherapy and biofeedback than their counterparts who did not believe that their own efforts could affect their health status. Following the assumption that locus of control is a manifestation of an underlying need, however, it was predicted that externally oriented headache patients would respond more favorably to the structure provided by biofeedback than would their internally oriented counterparts, whereas internals would fare better than externals in the relatively less directive arena of psychotherapy. Although the results were mixed, they tend on balance to offer differential support for the interaction hypothesis and hence for the formulation of locus of control as a reflection of an underlying need rather than as a superficial belief.