Pretreatment peripheral blood lymphocyte counts have been recorded in 181 consecutive untreated patients with histologically proven Hodgkin's disease and the patients followed prospectively to determine the relationship of lymphopenia to survival. Lymphocyte counts at presentation did not correspond with histology type but were lower in stage 4 disease. Survival in the 77 patients with lymphocyte counts of less than 1.5 X 10(9)/l was 49.7% which was significantly worse (P less than 0.0001) than the 74.2% survival of those with 'normal' counts. This difference was maintained even after adjustment for other acknowledged prognostic variables including sex, age, stage, symptom status, histology type, and response to treatment. The study provides evidence that the lymphocyte count can be used as a meaningful marker in the clinical staging of Hodgkin's disease.