Leucocyte migration inhibition detected in vitro by the capillary tube technique (LMCT) has proved a useful tool for detection of tumor-specific cell-mediated hypersensitivity (TCMH) in man. Investigations in pateints with renal tumors are reported. It is shown that TCMH is a feature of hypernephroma in man, that the antigenic specificity is found in autologous as well as allogeneic tumor tissue and in fetal kidney tissue. The pattern of reactivity compared to postoperative survival and occurrence of metastases and postoperative clinical course shows a clear association between TCMH and tumor elimination. The capacity of hypernephroma patients to develop a cell-mediated immune response is generally not reduced. In allogeneic combinations, small noninvading tumors usually have a high antigenicity, whereas tumors with early dispersion show a low antigenicity. The development of TCMH and associated tumor elimination therefore may be depending preferably on the antigenicity of the tumor, less on the immune capacity of the tumor host.