Microbial transformations were conducted with prosulfuron {1-(4‘-methoxy-6‘-methyltriazin-2‘-yl)-3-[[2‘‘-(3‘‘‘,3‘‘‘,3‘‘‘-trifluoropropyl)phenyl]sulfonyl]urea} to identify pathways by which the sulfonylurea herbicide is metabolized by microorganisms. Streptomyces griseolus produced four new hydroxylated metabolites which were isolated, chromatographically purified, and characterized by mass spectrometry and NMR spectroscopy as the following:  a benzyl alcohol from methyl hydroxylation on the triazine ring, phenolic and catechol metabolites by 3‘‘ and subsequent 4‘‘ hydroxylation on the carbocyclic aromatic ring, and a second benzylic alcohol obtained by microbial hydroxylation of the trifluoropropyl side chain. The new metabolites were used as analytical standards for soil incubation studies. Keywords: Prosulfuron; sulfonylurea; oxidative biotransformations; microbial metabolites; benzylic and aromatic hydroxylations; O-demethylation; hydrolysis