Progressive polyradiculopathy is a rare, well-documented complication of the acquired immunodeficiency syndrome in man. It has been commonly attributed to a cytomegalovirus (CMV) infection. We report two HIV-infected patients with clinical and electrophysiological features of a unique, subacute, progressive polyradiculopathy. Post-mortem examination in case 1 disclosed an infiltration of the leptomeninges, the lumbar spinal cord, and the anterior and posterior roots by a B-cell immunoblastic lymphoma. Immunochemistry for HIV1 and CMV was negative in the peripheral and the central nervous system. Case 2 showed bone-marrow involvement by a Burkitt type lymphoma. Specific chemotherapy was followed by both clinical improvement of the polyradiculopathy and complete remission on a second bone-marrow biopsy. These findings may indicate that a lymphoma must also be considered a possible cause of polyradiculopathy in AIDS.