Apo-salicylate hydroxylase from Pseudomonas putida S-1 has been crystallized by the dialysis method, using ammonium sulfate as the precipitant. The crystals belong to hexagonal space group P62 or P64 with unit cell dimensions of a = b = 142.8 Å and c = 63.8 Å, and diffract X-rays at higher than 3.5 Å resolution. A heavy-atom derivative has been prepared by soaking a crystal in an ammonium sulfate solution containing p-chloromercuriphenylsulfonate.