Abstract: A quantitative method for determination of the activity of nopaline synthase in the crude enzyme extract of crown gall by measurement of the expense of NADPH was established. The activity of this enzyme in vitro for the crown gall lines of potato, sunflower, tobacco and carrot induced by Agrobacterium tumefaciens carrying nopaline type Ti plasmid can represent its quantity in vivo for no any activitor or inhibitor of this enzyme for sixteen plant crown gall lines induced by four A.tumefaciens strains was measured by this rnethod.The quantities of this enzyme in all crown gall lines of carrot and tobacco including one of the single cell line of tobacco crown gall on the basis of DNA unit are ess viously than the quantity of it in all crown gall lines of sunflower and otato induccd by simillar A. tumefaciens strains.The different quantity of no- aline synthase in different host plants is determined to a great extend by the ifferent plants thomselves. It is possiblat that a cxterior gene incorporated into plant though Ti plasmid wi11 get different results in different plants.

Key words: quantitative, nopaline, synthase