Uredospores of wheat leaf rust did not take up or metabolize exogenous supplies of quinate-U-14C, shikimate-U-14C, p-coumarate-α-14C, or ferulate-α-14C. Caffeate-α-14C was converted to an unidentified ether-insoluble component which was recovered from the germination medium.Phenylalanine-U-14C and tyrosine-U-14C were readily taken up by uredospores of both rusts and were recovered from the solvent-soluble and insoluble fractions. No evidence for phenylalanine/tyrosine interconversion was obtained. Radioactivity was not incorporated into glycosides or free and bound esters of phenolic acids when phenylalanine-U-14C or tyrosine-U-14C were used as precursors. Radioactivity was not detected in free phenolic acids when uredospores were fed phenylalanine-U-14C. When tyrosine-U-14C was the precursor, radioactive p-coumarate was detected in the germination medium kept at 20 °C, and radioactive p-coumarate and caffeate were both recovered from the germination medium kept at 30 °C.Extracts of uredospores of wheat stem rust and wheat leaf rust contained shikimate dehydrogenase and tyrosine ammonia-lyase. Quinate dehydrogenase and phenylalanine ammonia-lyase were not detected.