The interaction of carcinoembryonic antigen (CEA) with Sepharose-bound concanavalin A (Con A) was used to devise a method of storing high-specific-activity 125I-CEA for prolonged use in radioimmunoassay systems. Antigenically active radiolabeled CEA bound strongly to Con A-Sepharose, whereas antigenically inactive radiolabeled degradation products were released from the beads and could be removed simply by washing the beads with buffer. The active 125I-CEA was eluted from the beads with O.1M α-methyl-n-manneside and could be used directly in the radioimmunoassay, since the glycoside did not interfere with antigen-antibody interactions. For example, one 125I-CEA sample (Initially ≈ 26μCi/μg), after storage without Con A-Sepharose for 72 days, could bind to CEA-specific antibody only to the extent of 49%, whereas the same antigen stored on, and eluted from, Con A-Sepharose exhibited 92% antibody-binding capacity. These data suggest the use of lectin-Sepharose conjugates for the storage of other radioiodinated glycoprotein antigens for similar purposes and the possibility of taking advantage of the binding properties of Con A-Sepharose for the isolation of CEA from tumor extracts.