Gram-positive Rhodococcus erythropolis strain S-1, grown in an aromatic carboxylic acid-salts medium, synthesized enzymes for the degradation of aromatic carboxylic acids, phthalate, monohydroxybenzoates, and dihydroxybenzoates. Flavoprotein-aromatic compound monooxygenases and dioxygenase from R. erythropolis, involved in the initial steps of the degradation pathways of aromatic carboxylic acids, were found in the membrane fraction. The enzymes in the membrane fraction were solubilized by Brij 58 or Tween 80 but denatured by Triton X-100. Solubilized and purified enzyme stability was conserved by Tween 80.