As morbidity of thrombopenia in hemophilia A patients is increasing, the pathogenetic influence of the reticuloendothelial system (RES) was measured using autologous anti-Rh0(D)-coated erythrocytes (EA) in 17 patients with or without thrombopenia. Mean survival of EA in patients was reduced to 53% of healthy controls (53.2 +/- 46.1 min vs 100.5 +/- 12.2 min; patients vs controls, mean +/- S.D.). Survival of EA was not significantly different either in thrombopenic vs non-thrombopenic nor anti-HIV (human immunodeficiency virus) positive vs negative patients. Thrombopenia, elevated serum IgG and circulating immune complexes were related to the presence of anti-HIV antibodies. EA survival was also decreased in the absence of anti-HIV antibodies. This indicates activation of RES by a mechanism different from retroviral infection by HIV (1).