We have compared the allergenicity of codfish and surimi (prepared from codfish) by skin testing, specific IgE-RIA, and leukocyte histamine release (LHR) in six fish-allergic patients. Prick tests were positive for codfish and, to a lesser extent, surimi. The percentages of labeled anti-IgE bound to surimi-Sepharose were 1.55 +/- 0.19% and 3-6% with control and patient sera, respectively. Inhibition of the surimi protein-Sepharose IgE-RIA was greatest (80%) at protein concentrations of 13.4 and 408.5 micrograms/ml for codfish and surimi extract, respectively. The allergenic protein was isolated by gel filtration and subjected to SDS-PAGE. The eluate from codfish contained several proteins ranging from 13 to 63 kDa, while the eluate from surimi contained a single 63-kDa protein. It was concluded that surimi contained a single allergenic protein.