Haloalkane dehalogenases are enzymes that release chloride or bromide from n-halogenated alkanes. X-ray quality crystals of haloalkane dehalogenase from the 1,2-dichloroethane-degrading bacterium Xanthobacter autotrophicus GJ10 have been grown at room temperature from 64% saturated ammonium sulfate solutions (pH 6.2 to 6.4). The crystals diffract in the X-ray beam to at least 2.4 Å resolution (1 Å = 0.1 nm). Their space group is P21212, with cell dimensions a=94.1 Å, b=72.8 Å, c=41.4 Å and α=β=γ=90°. There is one monomer (molecular weight 36,000) per asymmetric unit.