Esterases of the greenbug, Schizaphis graminum (Rondani), were investigated by polyacrylamide gel electrophoresis. Specific staining procedures or inhibitors were used to identify cholinesterases and carboxylesterases. Polyacrylamide gels incubated in alpha naphthyl acetate stained nine (P1-P9) esterase bands. The fifth and sixth bands stained darker when alpha naphthyl butyrate was used as a substrate. Band P1 was classified as a cholinesterase. Bands P2, P3, P4, P5, and P6 were classified as carboxylesterases. Results were inconclusive with respect to P7, P8, and P9.