The mean percentage of T and B lymphocytes in peripheral blood was tested in 6 patients with renal cancer before and after preoperative transcatheter embolization and radical nephrectomy. While no significant difference was found in B lymphocyte levels compared to those in healthy control subjects a clear impairment in circulating T lymphocyte levels was observed in renal cancer patients who had not been treated. This reduction in T lymphocyte levels persisted after embolization but there was a significant increase after radical nephrectomy.