Platelet activation is commonly monitored with a battery of monoclonal antibodies against different platelet epitopes with controversial results. The transient expression of platelet markers and their role mediating interactions with other cells could easily explain these discrepancies. The present study has evaluated whether the analysis of a leukocyte activation antigen (CD11b) could provide more reliable results than detection of platelet activation markers. Cytometric techniques with specific monoclonal antibodies were used to compare the reliability of platelet and leukocyte markers to detect activation. Modifications in the presence of platelet glycoproteins GPIb (CD42b), GPIIIa (CD41) and GPIV (CD36), expression of specific platelet markers (P-selectin (CD62P) and lysosomal protein (CD63)) and leukocyte integrin (CD11b) were assessed during hemodialysis. Platelet antigens remained in uremic patients at levels similar or slightly above those detected in a group of healthy subjects. Modifications of platelet antigens during hemodialysis produced inconclusive results. However, numbers of leukocytes expressing CD11b increased progressively during hemodialysis (17.2 +/- 5.1% at 15 min and 21.3 +/- 6.6% at 2 h, p < 0.05, vs. baseline 6.9 +/- 0.2%). The hemodialysis procedure caused an increased formation of leukocyte-platelet aggregates. Detection of leukocyte CD11b may be a useful marker of overall cellular activation during the hemodialysis procedure.