The screening of ten isoenzymes of two forms of Anopheles sinensis, Form A and B, using electrophoretic gels revealed that Est-5(96) allele was the marker in both 4th larva and adult female of An. sinensis Form B, whereas it was lacking in Form A. Hybridization tests of the two sinensis forms were done by induced copulation. The results of crosses indicated that they were genetically compatible, providing viable progeny and completely synaptic polytene chromosomes.