Many bacteria biosynthesize 3,4-dihydroxyphenylacetate 2,3-dioxygenases for growth on aromatic acids, but gram-negative organisms have been most extensively studied. A gram-positive strain containing 2,3-dioxygenase activity was identified as Arthrobacter strain Mn-1. The 2,3-dioxygenase from strain Mn-1 was purified to homogeneity by fast protein liquid chromatography with a Mono Q anion-exchange column. Rabbit polyclonal antidioxygenase antibodies were prepared. Ouchterlony double-diffusion and Western blotting (immunoblotting) protocols were used to probe the distribution of the Mn-1 dioxygenase antigen in soil bacteria. Fourteen 2,3-dioxygenase-containing Bacillus and Pseudomonas strains did not contain immunologically cross- reactive proteins. Six of eight Arthrobacter strains contained 2,3- dioxygenase activity, and all of them produced cross-reactive proteins. The data presented here suggest that a unique type of dioxygenase is geographically widespread but is taxonomically confined to Arthrobacter soil bacteria.