Abstract We have purified gamma-glutamyltransferases (GGT) from human kidneys and renal cell carcinomas, and fractionated them according to different lectin-binding properties of the isoenzymes. Native polyacrylamide gel electrophoresis and isoelectric focusing revealed different GGT-bands (even after desialylation) not only among kidney and renal carcinoma, but also among Con A-affine tumor fractions separated by ion-exchange chromatography. M r of native GGTs were between 106 to 161 kDa, the p I ranged from pH 3 to 4 (pH 5 to 6 after desialylation). Monoclonal antibodies to GGT were produced. One of these, of IgG 1 class and designed 138H11, recognizes human kidney GGT and, in addition, GGT from renal cell carcinomas and liver carcinomas. The specificity of mAb 138H11 for GGT was confirmed by Western blotting, by immunohistochemistry and by immunoprecipitation. The potential usefulness of mAb 138H11 in monitoring renal cancer patients and in identification of renal cancer metastases is currently being studied.