The expression of complement receptor type 1 (CR1) and type 3 (CR3) on polymorphonuclear leukocytes (PMNs) and generation of complement fragments, C3a, C5a, C4d, iC3b and Bb, were studied in patients during hemodialysis using cuprammonium rayon (Cu) membranes. Furthermore, the relation between the expression of CR1 and CR3 on PMNs from healthy donors and complement fragments was investigated. The expression of CR1 and CR3 on PMNs increased during hemodialysis. Plasma C3a, C5a and iC3b levels increased in the first 15 minutes and then decreased at 120 minutes of dialysis. But plasma Bb level remained high until the end of hemodialysis. Purified Bb had no effect on the expression of CR1 and CR3 on PMNs, but C5a augmented those expression in vitro. Nafamostat mesilate, an artificial proteinase inhibitor, inhibited augmentation of complement receptors on PMNs in concentration dependent fashion. C5a generated through the activation of complement was thought to take an important role in the increased expression of CR1 and CR3 on PMNs.