Patients with Hodgkin's disease (HD) or large cell lymphomas who relapse after conventional chemotherapy have a poor prognosis without high-dose chemotherapy and stem cell transplantation (HDCT). Patients who relapse after HDCT have an extremely poor outcome. In the present study we describe four patients with relapsed HD (n=1) and large cell lymphomas (n=3) after HDCT. All had an aggressive clinical course before HDT. At relapse, however, they all have had prolonged remissions and/or spontaneous regressions on mild or no treatment. Possible explanations could be selection of less malignant clones or a lymphoma controlled by the immune system. The mechanisms are, however, unknown but warrant further studies of the molecular biology in these and similar cases.