In Comamonas sp. strain P19, homogentisate 1,2-dioxygenase (HGO) catalyzes the conversion of homogentisate to 4-maleylacetoacetate by aromatic ring scission, in the breakdown of tyrosine and phenylalanine. To determine the molecular background of the enzymatic mechanism of HGO in this zinc-resistant organism, hmgA encoding HGO of Comamonas sp. strain P19 was cloned, and the expressed protein was purified. The protein was crystallized in solutions I [25% (w/v) polyethylene glycol 3350 and 0.1 M trisodium citrate at pH 5.6] and II [1.4 M ammonium tartrate and 0.1 M bisTris at pH 5.5]. X-ray diffraction data were collected to 1.8 ？ resolution using synchrotron radiation. The crystal belongs to the orthorhombic space group P212121, with unit cell dimensions of a？= 73.2 ？, b = 100.0 ？, and c = 134.9 ？. A traceable electron density map was calculated using anomalous diffraction data obtained from a crystal soaked in zinc ions.