Bacteriofcrritin-eytochrome from Azotobacter vinelandii is an unusual protein containinghaem groups as well as iron core like other ferritin. This paper reports tile purification of bacterioferritin by affinity chromatography and theformation of brick-red crystals from a solution containing MgCl_2. The crystals are opticalisotropic with maximum dimensions of 0.4×0.4×0.1 mm~3. The preliminary X-ray crystallo-graphic studies have boca performed. 1.5°unscreened precession photographs show that thecrystals of bacterioferritin belong to the cubic system, space group I432, with. cell dimen-sion 230 A. There arc probably 8 molecules in one cubic unit cell and the molecule might have 32symmetry. A molecular diameter of 115 A is derived from the packing of the molecules auda molecular weight of 826,000 is estimated for baeterioferritin. Bacteriofcrritin-eytochrome from Azotobacter vinelandii is an unusual protein containing haem groups as well as iron core like other ferritin. This paper reports tile purification of bacterioferritin by affinity chromatography and the formation of brick-red crystals from a solution containing MgCl_2. The crystals are opticalisotropic with maximum dimensions of 0.4 × 0.4 × 0.1 mm ~ 3. The preliminary X-ray crystallo-graphic studies have boca performed. 1.5 ° unscreened precession photographs show that thecrystals of bacterioferritin belong to the cubic system, space group I432, with. cell dimen-sion 230 A. There arc probably 8 molecules in one cubic unit cell and the molecule might have 32 symmetry. A molecular diameter of 115 A is derived from the packing of the molecules auda molecular weight of 826,000 is estimated for baeterioferritin.