Glutaminase from the marine bacterium Micrococcus luteus K-3 (Micrococcus glutaminase) is a salt-tolerant protein which shows equivalent activities both in the absence and the presence of 3 M sodium chloride and is distinct from halophilic proteins, which are inactivated in the absence of salt. To investigate the mechanisms of the salt-tolerant adaptation of Micrococcus glutaminase, the glutaminase and its major fragment containing about 80% of the protein were crystallized using the hanging-drop vapour-diffusion method. The glutaminase crystals belong to space group P622, with unit-cell parameters a = b = 111.4, c = 210.9 Angstrom, alpha = beta = 90, gamma = 120degrees, and diffract to 2.6 Angstrom resolution. The fragment crystals belong to space group F222, with unit-cell parameters a = 115.7, b = 116.4, c = 144.9 Angstrom, alpha = beta = gamma = 90degrees, and diffract to 2.4 Angstrom resolution. Data from selenomethionine (SeMet) substituted glutaminase crystals and from SeMet-substituted fragment crystals were collected to 2.6 and 2.4 A E resolution, respectively. Structural analyses of the glutaminase and its fragment are currently being attempted using the multiwavelength anomalous diffraction (MAD) phasing method.