Summary The role of 3-hydroxymethyl oxindole (HMO), a photooxidation product of indole-3-acetic acid (IAA), in stimulating elongation of wheat coleoptiles, increasing protein and RNA content and stimulating ethylene evolution was studied. HMO was found to be more oligodynamic than IAA. Unlike IAA, the growth promoting effect, increased content of protein and RNA induced by HMO, remained unaffected after pretreatments of the coleoptiles with chemicals inhibiting oxidation of IAA. No stimulation of ethylene evolution was detected either with IAA or with HMO, following pretreatments. A possible cause of this inhibition is discussed. Much more pronounced increases in protein, RNA and even DNA were observed by application of HMO than with IAA in seedlings. HMO induced more ethylene evolution than IAA in both wheat seedlings and coleoptile sections. The changes in the level of IAA-metabolic enzymes, viz. IAA-oxidase, peroxidase and methyleneoxindolereductase were studied after the application of IAA and HMO, with or without pretreatments. The changes in the level of IAA and IAA-metabolic enzymes with age were also studied in shoots and roots of developing wheat seedlings. The possible role of HMO in auxin mediated actions are discussed.