We report here a rare case of pure red cell aplasia (PRCA) following autoimmune haemolytic anaemia (AIHA). After 4 years of AIHA, the patient developed anaemia with severe erythroid hypoplasia and was diagnosed as having PRCA. At this time, Coombs’ test was negative and parvovirus infection was not recognized. The patient received azathioprine, and PRCA improved. To determine the pathogenesis of PRCA, in vitro culture studies of erythropoietic and granulopoietic precursors were performed. The patient’s serum or IgG did not suppress the colony formation of bone marrow colony-forming units-erythroid (CFU-E) of normal subjects and the patient. In contrast, mononuclear cells in the peripheral blood of the patient significantly suppressed CFU-E of normal subjects. Media conditioned by the patient’s mononuclear cells did not significantly suppress CFU-E. The significant production of suppressive cytokine such as tumour necrosis factor or γ-interferon by the patient’s mononuclear cells was not recognized. These findings suggest that the cytotoxic mononuclear cells affected directly the erythropoietic precursors and caused PRCA in this patient. The pathogenesis of PRCA was, therefore, considered to be different from that of the preceding AIHA.