A new method for the isolation of p53 protein from the sera of cancer and non-cancer patients has been developed. The method is based on the utilization of a new modification of a support for affinity chromatography in the form of gel fiberglass (GFG) (R. Zusman, patent applications, Israel, 1992; USA 1993). The sera were percolated through GFG columns with entrapped rabbit IgG generated against the colon cancer antigens. Tumor-associated antigens were eluted from sera of cancer patients in large amounts, up to 2.4 mg/ml serum/column. Concentrations of these antigens in different sera and their affinity to anti-tumoral antibodies were detected by ELISA. Western immunoblotting with commercial monoclonal antibodies and SDS-PAGE identified the isolated antigens as the p53 protein. This protein has been isolated in the highest concentration yet reported from the serum of cancer patients, up to 1 mg/ml. The same protein has been found in the serum of healthy people and non-cancer patients but in significantly lower concentrations. Isolation of p53 protein from sera of noncancer patients confirms the opinion of some investigators that this protein should be considered not only as an oncogene but also as a protein correlated with different changes in the cell cycle.