Various strains of Escherichia coli (but not strain K-12) were found to grow on 3-hydroxyphenylacetate and 4-hydroxyphenylacetate. Both compounds were catabolized by the same pathway, with 3,4-dihydroxyphenylacetate as a substrate for fission of the benzene nucleus, and with pyruvate and succinate as products. All the necessay enzymes were demonstrated in cell extracts prepared from induced cells but were essentially absent from uninduced cells. Mutants unable to grow on 3- and 4-hydroxyphenylactetate were defective in particular enzymes of the pathway. The characteristics of certain mutants indicated that either uptake or hydroxylation of 3- and 4-hydroxyphenylacetate may involve a common protein component. E. coli also grew on 3,4-hydroxyphenylacetate, with induction of the enzyme necessary for its degradation but not those for the uptake-hydroxylation of 3- and 4-hydroxyphenylacetate.