Crystals of alpha 1-acid glycoprotein have been grown reproducibly from delipidated protein in the presence of chlorpromazine. The crystals are large hexagonal prisms of space group either P622 or P6(2)22 and the unit cell dimensions are a = b = 101 A and C = 201 A. The unit cell is very highly hydrated and is nearly 80% solvent. It contains one molecule of protein per asymmetric unit. The crystals diffract only to low resolution, presumably reflecting the extensive hydration and accompanying disorder.