The meat ant (Iridomyrmex purpureus) occurs in a number of color forms, with uncertain taxonomic status. Gel electrophoresis of meat ant extracts, followed by nonspecific esterase staining, reveals several zones of activity. Allelic variation at three loci is proposed to account for variation in some of these zones. Two of the loci (Es-1, Es-2) appear to have recessive null alleles, whose frequencies have been estimated by the method maximum likelihood. Geographic variation in allele frequency is attributed to behavioral and geographic subdivision of the population. Apparent disturbances segregation ratios and deviations from Hardy-Weinberg equilibrium can be accounted for if it is argued that some nests contain more than one queen. Differences in gene frequency between sympatric populations of the red and blue forms of I. purpureus are observed, confirming their reproductive isolation and sibling species status.