Knowledge of the prognostic factors that characterize a disease can assist in planning and analyzing clinical trials. The present study was conducted to determine the characteristics related to response and survival in patients with stage III and IV non-Hodgkin's lymphoma who were treated with combinations of cyclophosphamide, vincristine sulfate, and prednisone. Considering each characteristic individually and using stepwise regression analysis, tumor bulkiness, prior therapy, sex, and pretreatment lymphocyte count were selected as the four most important prognostic variables. Tumor architecture (diffuse or nodular pattern) and cell type, hemoglobin level, and symptoms although not important in predicting response were found to be important in predicting survival. The hemoglobin level had only marginal importance in predicting response. Factors found not be important were age, stage, symptoms, cell type, nodularity, marrow involvement, prior extensive radiotherapy, and bone involvement. A logistic regression equation has been derived that can be used to predict response rate.