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Abstract. Six dichlorophenoxyacetones were synthesized and examined as potential meta,bolic antagonists utilizing A vena coleoptile sections and the straight growth assay procedure. Supplements of indoleacetic acid promoted growth of the sections which were inhibited by the anailogs; the most inhibitory derivatives were 2,3-; 2,4-; 2,5-; and 3,4-diohlorophenoxyacetone which produced half-maximal growth responses (relative to the unaugmented oontrol growth) at concentrations of 106, 86, 80, and 62 mg/ml, respectively. A Lineweaver-Burk plot of the data for the inhibition by 2,4-dichlorophenoxyacetone and its reversal by indoleacetic acid appeared to represent an uncompetitive-like inhibition.A conisiderable aimount of research has been directed toward elu-cidaiting a relationship between chemical structure and pJant gro'wtih activity of auxin-like compound4s. Mulclh of th,i!s work has concerned aryloxy acids and their derivatives, especially 2,4-dichloroqhenoxyace,tic acid (13). Studies on the lAant physiological actions of these types of compounids have been numerouts (11), but the mode of biochemical action of these suvbstances rem,a,ins oibscu,ire. In an effort to appr,oac;h this problem from a posisible mOtabollite-analog relationshi,p (9), wifth tihe antici,pation of uttidlizing inhihitio-n analysis techniiquies (10), a series of dichilorophenoxyacetones were prepared and examined as antagonixsts of inldoleacetic acid itl anl Aena coleoptille assaya system (12).