The leukocyte migration inhibition test (LMIT) was used in eight patients with endometrial adenocarcinoma in order to evaluate the presence of a cell-mediated immune response to a soluble tumor extract. In three of four patients with tumor confined to the uterine cavity the LMIT was initially positive. Six to nine months after therapy a repeated LMIT was found to be negative. A negative LMIT was found in the other four patients with tumor extending beyond the uterine cavity. Negative assays were obtained when a homologous tumor extract with a positive autologous reaction was tested against leukocytes from two patients with extended disease. The possible significance of these findings is briefly discussed.