In the present study the role of sCD23 determination in the management of renal graft recipients during the early postoperative period has been evaluated. In the majority of patients, increases in sCD23 serum levels were observed up to 3 days before the manifestation of an acute rejection (in 82% of cases) or infection episode (in 73% of cases), but no discrimination between these two clinical events was possible. This rise in sCD23 levels was significantly more pronounced than fluctuations observed in patients with uncomplicated courses or with graft dysfunction due to acute tubular necrosis. Serum levels of sCD23 were not influenced by excretory kidney function. These findings indicate that, in addition to its reflecting B-cell function, sCD23 may also play a role in immunological processes involving T cells and/or monocytes, thus indicating a broader range of activity of this cytokine-like molecule than has been previously assumed.