Perceived control has become an important construct for health care research. Since the processes and outcomes of health and illness are constantly mediated and affected by communication, the relationship between a person's belief in his/her personal control of events and health care interactions is an important component of the theory and practice of health communication. An examination of the research literature on the relationship between locus of control and resistance to influence reveals important differences in terms of how internals and externals respond to influence attempts. While externals may expect to be passive receivers of treatment and advice, overly directive approaches may challenge the internal to sabotage treatment outcomes unless he/she is an active participant in planning and executing treatment. Externals may resist specific knowledge of their condition, while internals may respond poorly unless given specific information. The amount of structure or controllability in a treatment situation may facilitate or impede the progress of treatment, depending upon its congruence with the patient's control expectancies. The control style of caregivers is at least tacitly present in their intervention/message style and enthymematically interacts with the patient's worldview to influence the patient's expectation for success. There is some evidence to suggest that congruent control messages facilitate actual treatment success as well. (Footnotes are included and 151 references are attached.) (RAE)