The serum concentrations of soluble interleukin-2 receptors and urine neopterin were studied in 82 patients with malignant lymphomas (25 patients with Hodgkin's disease and 57 patients with non-Hodgkin's lymphoma. Increases in soluble interleukin-2 receptors and in urinary neopterin were significantly correlated with the clinical phase of the disease. The average values in both Hodgkin's disease and non-Hodgkin's lymphoma patients suffering from the disease in its active phase were significantly higher than those of patients in complete remission. Neopterin concentrations (but not soluble interleukin-2 receptor concentrations) were also elevated in clinical stages III - IV of each disease. Urinary neopterin correlated directly and significantly with the erythrocyte sedimentation rate and inversely with haemoglobin. Finally, a longitudinal analysis showed a general tendency for the markers to return to normal values, in accordance with the favourable outcome of therapy; this was more evident for urinary neopterin than for soluble interleukin-2 receptors. These findings seem to confirm that soluble interleukin-2 receptors and especially urinary neopterin can be useful markers for monitoring and prognosis of malignant lymphomas.