The oxygenating constituent of the 3,6-diketocamphane monooxygenase isozyme from Pseudomonas putida NCIMB 10007 has been crystallized under two different conditions. Crystals were initially grown from polyethylene glycol (PEG) 8000 and sodium acetate using the vapour-phase diffusion method. The crystals were of orthorhombic P212121 space group, with cell dimensions a = 55.8, b = 94.5 and c = 163.7 A and diffracted to 2.8 A resolution. More recently, improved crystals, which diffracted beyond 2 A, have been grown from ammonium sulfate. These crystals also belong to the orthorhombic P212121 space group, with cell dimensions of a = 54.6, b = 93.2 and c = 154. 1 A. A full native data set to 2.5 A resolution has been collected from the ammonium sulfate grown crystals.