Two new crystal forms of isoenzyme 3-3 of rat liver glutathione S-transferase (GST 3-3) have been obtained. They were grown under essentially the same crystallization conditions as those reported for the C2 crystal form [Fu, Rose, Chung, Tam & Wang (1991). Acta Cryst. B47, 813-814]. The new crystals belong to space group P2(1) with one form having cell dimensions a = 101.6, b = 69.5, c = 81.4 A, and beta = 113.6 degrees, and the other form having cell parameters a = 97.4, b = 81.1, c = 69.4 A and beta = 109.2 degrees. These new crystals diffract to at least 2.5 A, resolution. The molecular packing arrangements in these P2(1) crystals have been found by molecular replacement studies.