Sarcoplasmic proteins were isolated from skeletal muscle of 14 species of Gulf of Mexico sciaenids encompassing 11 genera utilizing isoelectric focusing (lEF). Individuals from the 11 genera were distinguishable. However, intrageneric comparisons (Cynoscion and Menticirrhus) were constrained by similar protein banding among congenerics and required a high resolution pH gradient (pH 4-5) to produce species-specific patterns. A graphical representation of differences in banding patterns among the 14 species was provided by densitometric tracings. Isoelectric focusing provided qualitative evidence of the biochemical relationships among and within the 11 genera surveyed. Although only 2 multi-species genera were surveyed, this study appears to confirm their status as congenerics. Protein profiles generated by IEF appear superior to conventional electrophoretic techniques for the identification of certain sciaenid species. Discrepancies between results of allozyme and isoelectric focusing surveys concerning sciaenid systematics have been identified.