Cancer is still a threat to human beings. The incidence and mortality rate of cancer have been gradually increasing as the life span has been lengthened. Radiotherapy is one of the most commonly used treatments for cancer. This study explored the influence of social support and stress on sick role behavior of patients receiving radiotherapy for cancer. The subjects for this study were 60 patients undergoing radiotherapy for cancer, selected from the radiotherapy treatment unit of the out patient departments of two major medical centers in Jeonju. Data were collected from February 1 to 28, 1990 by a Likert Scale Questionnaire and an interview schedule designed by the investigator. Data analysis included percentages, mean and standard deviation, to or F-test, Pearson Correlation Coefficient and stepwise multiple regression. Results included the following : 1. Support came primarily from sons and daughters(90.1%) ; the type of support was primarily emotional support from friends(60.0%) ; information support came from health personnel(81.7%) ; and material support was sons and daughters(40.0%) ; satisfaction with support was highest for the spouse(4.02+/-.52). 2. Among the patient's demographic status was occupation the was the only socioeconomic characteristic influencing sick role behavior(F=2.91, p=.029). 3. Directly perceived support was positively correlated with sick role behavior(r=.2374, p=.034). 4. Stepwise multiple regression was used to determine the predictors of sick role behavior. Directly perceived support was the most significant predictor accounting for the highest contribution to sick role behavior(5.6%). Directly perceived support, socioeconomic status, perceived stress and indirectly perceived support variables together, accounted for only 6.8% of sick role behavior.