A rapid method is described for fish species identification by agarose gel isoelectric focusing (AGIEF). The AGIEF method can be completed in less than 2 h and gives reproducible species-specific sarcoplasmic protein patterns. Protein patterns are similar using either centrifuged tissue fluid or muscle tissue as the sample. One species, monkfish (Lophius americanus), has a polymorphic protein pattern. A predominant pattern was found in 66.7% of the individuals; 2 variant patterns were equally distributed among the remaining 33.3%. AGIEF offers a more rapid, less expensive alternative to the current AOAC official first action method for fish species identification based on polyacrylamide gel isoelectric focusing.