Cucumber seeds were germinated in Petri-dishes for 6 days with different doses of a number of N-monosubstituted amide derivatives of some chloro phenoxy-alkane-carboxylic acids. Doses of the amides studied were roughly equivalent to o-i, i, 10, too, and i,ooo p.p.m. in water. The gross morphological effects of the amide treatments were studied, both with and without the addition of i and io p.p.m., respectively, of the corresponding carboxylic acid. The amides studied were the N-methyl-, N-ethyl-, N-propyl-, N-iso-propyl-, N-butyl-, and N-benzyl-amides of 2,4-dichlorophenoxyacetic acid (2,4-D), a-(2,4-dichloro phenoxy)-propionic acid (2,4-DP), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and a-(2,4,5-trichlorophenoxy)-propionic acid (2,4,5-TP). Thirteen of the twenty-one amide derivatives studied antagonized the auxin type plant-growth-regulating effects of their parent carboxylic acid. The anta gonisms observed involved not only a decrease in the stimulatory effects of the externally applied auxin acids (counteractions of the abnormal swellings of different plant parts), but also reduced significantly their inhibitory effects, i.e. the inhibitions of growth in length of the hypocotyl and of the roots. Since some auxin-type stimulatory effects were observed with all of the amides studied, it is suggested that the thirteen amide derivatives play a double role as plant growth regulators in cucumber tissues: (1) to a certain extent they are transformed by plant enzymes to the corresponding carboxylic acid, i.e. to auxin; and (2) the amides themselves exert anti-auxin effects.