The binding of Ulex europeus agglutinin-I (UEA-I) and Peanut agglutinin (PNA) was studied in 56 endometrial carcinomas. The positive rates of UEA-I and PNA were 66%. Following neuraminidase treatment, the PNA positive rate increased from 66% to 98% and most tumors stained abundantly. UEA-I staining was unaffected. Using a combined grading system based on architectural and nuclear abnormalities, the PNA positive rates of grade 1, grade 2 and grade 3 tumors were 78%, 70% and 36%, respectively. There was no correlation between UEA-I binding and the grading systems. UEA-I binding correlated significantly with the presence of myometrial invasion and vessel permeation. Metastatic endometrial carcinomas showed a high affinity of tumor cells for UEA-I. Tissues that stained with UEA-I were those from patients with the worst prognosis. PNA and UEA-I reactivities relate to the biologic activity of endometrial carcinomas. UEA-I can serve as a prognostic marker for patients with endometrial carcinoma.