Crystals grown from a 60-kDa isoallergen mixture of Bermuda grass pollen have been obtained in 30% PEG 4000 and 25% isopropanol. The crystals diffract beyond 2-Angstrom resolution and belong to a tetragonal space group with the unit cell dimensions a = b = 86 Angstrom and c = 310 Angstrom. The preferential crystal growth of the larger isoallergens with a blocked N-terminus indicates that crystallization can isolate proteins with compact conformation.