Alcohol oxidase from Pichia pastoris has been crystallized from polyethylene glycol 4000 solutions. The crystals are tetragonal, a = 228 A, c = 456 A space group P4(1)2(1)2. The crystals scatter only to about 6 A resolution; their poor crystallinity may have some physiological function. Secondary structure predictions suggest that the C-terminal part of the molecule, residues 311-664, has the folding of an eightfold beta/alpha-barrel (TIM barrel). This would indicate common ancestry with four other flavoenzymes: canavalin, glycolate oxidase, flavocytochrome b, and trimethylamine dehydrogenase.