Amino acid incorporation into plasma membrane proteins of Vigna sinensis (L) was inhibited by malathion, an organophosphorous insecticide, whereas some stimulatory effect was elicited by plant growth hormones, viz., IAA, GA3 and kinetin. The inhibitory effect of malathion towards amino acid incorporation into plasma membrane proteins was marked at concentrations above 50 ppm, and at 400 ppm the amino acid incorporation was much less. Up to 100 ppm of malathion treatment, the plant growth hormones could counteract the malathion-induced inhibition on amino acid incorporation into plasma membrane protein but above this concentration, the plant hormones gradually lost their effectiveness. Plasma membrane fraction was characterized by studying the activities of enzymes like IDPase, Oligomycin treated ATPase, Cytochrome c-oxidase and glucan synthetase, and also by a sterol/phospho lipid ratio study. From the above studies it appears that glucan synthetase may be the marker enzyme of the plasma membrane of V. sinensis (L), and some change at the membrane level on malathion exposure is suggested. © 1981, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.