Genetic variation in four populations of the mussel Perna perna (L), from the shores of northeast Venezuela was studied using starch gel and polyacrylamide gelelectrophoresis. Twenty five protein systems were examined representing 23 loci, of which only 4 (12.50 %) showed polymorphism (LAP, ES, PGM, Y PGI). The number of alletes per locus varied from 1 to 3, with a mean 1.16. Each individual was heterozygous at 5.2% of its loci and the number of effective alletes was 1.06. The populations analysed were closely similar. Changes in gene frequencies in the four polymorphic loci were also studied in the six year period of the study.