The purified alpha -amylases from mucoid and non-mucoid B. amyloliquefaciens strains were crystallized in forms suitable for X-ray diffraction analysis. Crystals were grown by the hanging-drop vapor diffusion method. Very thin crystals of alpha -amylase of non-mucoid strain were obtained in the presence 15% propanol, 12% PEG 6000 and 0.1 M PIPES (pH: 7.1) at the end of 3 months and these were not suitable for X-ray diffraction analysis. Crystals of the mucoid strain of B. amyloliquefaciens alpha -amylase were obtained with 30% PEG 6000, 0.2 M (NH4)(2)SO4 and 0.1 M PIPES (pH: 6.5) at the end of 3 months and these were suitable for X-ray diffraction analysis.