Abstract: The patterns of esterase (Est) isoenzyme of 3 flea species were studied by vertical slab polyacrylamide gel e.ectrphoresis (PAGE). The samples prepared from the third larval ins-tar, female and male (the unsucking and sucked one) were run in the same gel slab. The result was as follows: Xenopsylla cheopis showed 14 bands, with 5-6 major bands, Cte-nocephalides felis felis showed 9 bands with 4-5 major bands and Nosopsyllus laeviceps kuzenkovi showed 9 bands with 4-5 major bands. These three species have their common bands as well as respective specific bands. The difference in Est isoenzymogram among families was greater than among genera, displaying a species-specific feature (Figs. 1-4).