The non-Hodgkin's lymphomas represent an area of rapid medical progress. Recent studies of staging have suggested that with respect to therapy disease is either limited (stage I or II) or advanced (stage III or IV). Bone marrow biopsy is important as an initial staging tool, and retroperitoneal evaluation (lymphangiography, ultrasound) is important when marrow involvement is not present and also as a means of establishing a baseline for clinical evaluation. For patients with nodular lymphoma, combination chemotherapy can produce high rates of complete remission, but relapses occur and survival has not been shown to be improved as compared to patients receiving single-agent therapy; the value of therapy in asymptomatic patients is not established. In contrast, advanced histiocytic lymphoma, which is rapidly fatal when single-agent therapy is used, is cured in half of patients receiving new combination chemotherapy regimens. While clinical discussions must use the Rappaport system of pathologic classification, because most data have been expressed using this terminology, it should be recognized that immunologic approaches to the classification of lymphoma exist, and that their clinical utility is undergoing evaluation.