Papaya mosaic virus coat protein has been treated with trypsin and a large fragment of the intact protein has been crystallized in space group P3(1)21 or P3(2)21 (unit cell dimensions: a = b = 110 A, c = 237 A). The crystals diffract to 3.5 A resolution. Crystals of the untreated protein have also been grown. The untreated protein crystals diffract to 4 A resolution, but have a large mosaic spread. They have the same space group as the trypsin-treated protein crystals, but a much smaller unit cell (a = b = 72 A, c = 240 A).