Using in vitro techniques, bone marrow (BM) function has been studied in 25 patients in complete remission and at least one year after the completion of MVPP chemotherapy for Hodgkin's disease. The numbers of granulocyte/macrophage (GM-CFC) and fibroblastoid (CFU-F) progenitors were significantly lower than controls and there was no evidence of any improvement with time (median months off treatment was 30 for GM-CFC and 34 for CFU-F). In long-term BM culture production of haemopoietic cells were strikingly lower in the post-MVPP group and the development of adherent stromal cell populations was also significantly less. In addition, the yield of GM-CFC in adherent layers after four weeks of culture was significantly lower than in controls. We conclude that following MVPP chemotherapy and in apparently disease free and haematologically normal individuals there is evidence of impaired BM function up to nine years after the completion of treatment. These abnormalities may be relevant to the known increased risk of acute non-lymphocytic leukaemias in this group of patients and are likely to render the BM less able to withstand subsequent insults such as further chemotherapy or infection. The eventual development of BM failure is also a possibility and long-term follow-up of these patients is essential.