Evidence is presented that at least one of the antigens of human ovarian cancer tissue which appeared to be tumor-associated in immunodiffusion and immunoelectrophoresis experiments actually represents a quantitative rather than a qualitative difference between normal and malignant tissue. A glucoprotein band (Rf equals 0.01) believed to contain at least one tumor-associated antigen was isolated by disc-gel electrophoresis with 5.6 per cent SDS-acrylamide and was used to immunize rabbits. Immunodiffusion and immunoelectrophoresis experiments with the resulting antiserum indicated that the glycoprotein band contained two antigens, one which was present in normal extracts at a concentration approximately one tenth of that in tumor extracts and another which was detectable only in tumor tissue. The tenfold difference between normal and tumor tissue was confirmed by studies of the appearance and disappearance of the glycoprotein band when acrylamide gel electrophoresis was performed on varying amounts of normal and tumor extracts.