Two different assays were employed to assess the suppressor cell activity of peripheral blood mononuclear cells (PBMC) from 38 patients with Hodgkin's disease (HD) and 40 control subjects. The response to phytohemagglutinin (PHA) was also measured. Depressed PHA reactivity was found in all groups of patients irrespectively of stage, histologic type or symptomatic status. Increased indomethacin-sensitive suppressor cell activity (ISSCA) was observed only in patients with B-symptoms. In contrast, the coculture suppressor cell activity (CSCA) was markedly elevated in all groups of patients. This parameter did not correlate well with the clinical features of the disease. Splenocytes from eight patients with HD responded to PHA better than PBMC, but the difference was not statistically significant. The spontaneous DNA synthesis in splenocytes from patients with HD was 9 times higher than in PBMC. Highest values of spontaneous DNA synthesis were observed in spleens with tumor involvement. Both suppressor cell assays failed to detect a significantly increased suppressor cell activity in the spleen. A normalization of the increased CSCA was seen after splenectomy.