The records of 637 patients with lymphoproliferative disorders and 346 patients with myeloproliferative disorders were retrospectively analysed for the presence of additional autoimmune derangements. The frequency of autoimmune perturbations in lymphoproliferative diseases (51 cases; 8.0%) was significantly higher than in myeloproliferative diseases (six cases; 1.7%; P less than 0.0001). Rheumatic disorders, autoallergic haematological manifestations and other organ-specific autoimmune derangements were responsible for about one third each of the observed disturbances. Autoimmune diseases which preceded the onset of malignancy, occurred in lymphoproliferative and myeloproliferative disorders with a comparable frequency without significant differences between individual subgroups of lymphoproliferative diseases. In contrast, autoimmune complications developing in the course of the neoplastic disease were significantly more frequent in lymphoproliferative (4.9%) than in myeloproliferative disorders (0.3%; P less than 0.0005). Here marked differences were observed between individual lymphoma entities, the rate of concomitant autoimmune derangements ranging from zero to over 15%. With the exception of centroblastic-centrocytic lymphoma which in no case was associated with secondary autoimmune complications, the proportion of patients with autoimmune perturbations increased with improving prognosis of the lymphoproliferative diseases. Possible pathogenetic mechanisms involved in the manifestation of autoimmune complications in malignant lymphomas are discussed.