Immunosuppression with pATGs may influence the expression of adhesion molecules on thrombocytes, lymphocytes and neutrophils due to unspecific antibodies directed against myeloid and nonmyeloid cells. The aim of our study was to assess the influence of pATGs upon the in vitro expression of adhesion molecules of lymphocytes, neutrophils and thrombocytes by means of flow-cytometry. Depletion, activation and expression of adhesion molecules of thrombocytes (CD41, CD42, CD62p, CD107a), neutrophils and lymphocytes (CD11, CD18, CD62L) were studied in vitro in whole blood of healthy volunteers by means of flow cytometry after incubation with standard and toxic doses of three polyclonal ATGs: ATG-Fresenius(S); Thymoglobulin and Tecelac.Our data show no ATG-mediated cytotoxical activity against platelets. ATGs are able to activate platelets through increased expression of P-selectin and hLAMP-1. ATGs also reduce the expression of CD62L on lymphocytes and neutrophils. Furthermore, the effects of ATG on CD11/CD18 are dependent on the dosage and the ATG employed.Our data show that ATGs induce expression of adhesion molecules and activate unstimulated thrombocytes as well as reduce the expression of adhesion molecules on lymphocytes and neutrophils. Increased adhesion of thrombocytes may be responsible of side-effects observed in the clinical practice such as decreases of circulating thrombocytes and haemorrhages. Reduction of the expression of adhesion molecules of lymphocytes and neutrophils can increase the risk of infection.