Indole-3-butyric acid (IBA) was metabolized by seedlings of Arabidopsis thaliana cultivated in liquid medium under sterile conditions to two major metabolites. One metabolite was hydrolyzed by 1 N NaOH and β-glucosidase and was tentatively identified as IBA-glucose and the other was hydrolyzed by 7 N NaOH and amidase and was identified as an amide-linked conjugate. IBA-glucose synthase activity was found in a soluble enzyme fraction after incubation of ³H-IBA, IBA and UDP-glucose. The labelled reaction product had an R_f value comparable to IBA glucose and stained positive with Ehmann reagent.