Abstract: An investigation on the isozyme patterns of esterase and malic dehydrogenase of Periplaneta japonica,Periplaneta fuliginosa,Blattella germanica and Periplaneta americana was done.Though all revealed 6-7 bands,yet all these 4 indoor species show significant differences in the Rf value of esterase isozymes.Malic dehydrogenase gives 3 or 4 bands,showing some species-difference,but not so obvious as seen in esterase.Blattella germanica is much more different from the rest 3 species.The significance of these findings needs further elucidation.