An immunosorbent column was prepared containing a purified major allergen fraction from codfish (DS 22) covalently coupled to agarose. Sera from patients allergic to codfish were run through the column at pH 7.2. After extensive washing, the IgE retarded in the column was eluted with a buffer at pH2.5. The original sera and fractions from the chromatography experiments were examined by means of crossed immunoelectrophoresis (CIE), crossed radioimmunoelectrophoresis (CRIE), radioallergosorbent test (RAST) and in vivo passive transfer (PK) tests using the DS 22 from codfish and a crude codfish extract. The experiments demonstrated that the crude extract contained a minor codfish allergen (antigen-17-cod) which was distinct from DS 22. RAST was the most convenient technique for the identification of fractions containing allergenic activity. The PK tests served to prove the biological activity in vivo. CIE/CRIE were superior to RAST and PK tests regarding their ability to identify distinct allergens. Full agreement was found between results using different techniques including the immunosorbent experiments. Some of the radiostaining in CRIE, however, was misleading due to coprecipitation of DS 22 in several precipitates in the CIE preparations of the crude codfish extract.