Serum ferritin has been estimated in 125 untreated patients with Hodgkin's disease. Increasing concentrations are found at each advancing stage of the disease and high concentrations are found in patients with systemic symptoms. In all cases this is associated with a low serum Fe concentration and reduced transferrin saturation. There is no relationship between serum ferritin concentration and histological type of disease. The findings are compatible with a non-specific response of the reticuloendothelial system to malignancy, producing a secondary disorder of Fe metabolism.