The sarcosine oxidase from Bacillus sp. NS-129 has been crystallized by vapor diffusion using ammonium sulfate as precipitant. The tetragonal crystals have P4(1)2(1)2 (or P4(3)2(1)2) symmetry with a = b = 177.0 and c = 72.6 Angstrom. The crystals probably contain two sarcosine oxidase molecules per asymmetric unit and diffract to at least 2.7 Angstrom resolution. (C) 1997 Academic Press.