Four cases of pure red-cell aplasia (PRCA) in association with chronic lymphocytic leukemia (CLL) are summarized. In addition, all reported cases of CLL-PRCA (27, including our 4 cases) are reviewed to consolidate their clinical features and compare them with those of 26 patients with CLL who were anemic (Stage III) and 52 who were not anemic (Stages O-II). The incidence of PRCA in our patients with CLL is about 6%. Eighty-seven percent of patients with PRCA had B-lymphocyte (B-cell) CLL and 13% had T-lymphocyte (T-cell) CLL. In 4 of 17 patients PRCA was the presenting feature, and in 13 of 17 it developed in patients previously diagnosed as having CLL. In the latter group, the average time from the diagnosis of CLL to the development of PRCA was 50.2 months (range, 1 to 96). The average age at presentation with PRCA was 61.6 years (range, 37 to 79), and the male to female ratio was 1.6 to 3:1. Eighty-one percent had splenomegaly and 65% had lymphadenopathy. The average hematocrit was 17 +/- 3.6% with zero reticulocyte count, and the lymphocyte count was 134 X 10(3)/microliter. Normoblasts were absent in the marrow and lymphocytes constituted 50 to 100% of the marrow cells. In patients with B-cell CLL and those with T-cell CLL, the T cells were found to inhibit the growth of the marrow erythroid progenitors in in vitro cultures. These abnormal T cells (Tr cells) possessed IgG Fc receptors on their surface, which may be responsible for induction of PRCA in these patients. Continued administration of cyclophosphamide and prednisone in moderate doses appears to induce remission from PRCA, but not until the leukemic mass and abnormal Tr cells are markedly reduced. Daily or alternate-day cyclophosphamide administration in small to moderate doses seems to be essential to maintain remission.