The objectives of this Project are to examine a theoretically based model of social factors hypothesized to contribute to the perpetuation of illness behaviors and functional disability in patients with chronic fatigue syndrome (CFS). Cognitive-behavioral models of chronic illness have posited the response of significant others may contribute to the maintenance of illness behaviors and disability through social reinforcement. This model has received empirical support in studies of chronic pain patients using similar methods to those proposed here. It does not imply that the symptoms of illness are not present or "real" or are a conscious manipulation of the social environment. Rather through learning mechanisms, illness behaviors may be influenced by social responses, particularly solicitous responses by partners in intimate relationships, leading to disability beyond that associated with pathophysiology. To test this model, 100 patients with CFS and their partners will be videotaped while participating together in a standardized, validated protocol of tasks designed to simulate typical home activities. The videotapes will be coded by trained observers using a reliable and valid coding system to yield data on patient illness behaviors. The patient and partner will also complete questionnaires on patient functional disability, illness behaviors, relationship satisfaction, mood, attachment style and perceptions regarding the patient's illness and partner responses. Patients also complete a step test to measure physical fitness and rate their fatigue and pain. Six months later, patients and partners will complete questionnaires on current functional status and intervening treatments. This Project will address these questions: Are partner solicitous responses to CFS patient illness behaviors associated concurrently with more patient illness behaviors and disability and less physical fitness, and longitudinally with greater patient illness behaviors and functional disability? Do patient and partner perceptions, attachments type or relationship satisfaction influence the relationships between partner solicitous responses and patient illness behavior, functional disability and fitness? Our results could identify factors that perpetuate functional disability in CFS and pave the way for developing psychosocial treatments involving both the patient and partner to decrease the impact of CFS on patient functional disability.