Trichosanthes kirilowii lectin 1 (TKL-1) isolated from the tuber of T. kirilowii consists of two chains, each with a molecular weight of about 30 kDa. It has immunological properties which are similar to some ribosome-inactivating proteins (RIPs). TKL-1 was crystallized in space group P2(1)2(1)2(1) and diffraction data were collected to 2.7 A resolution. The molecular-replacement method was applied to solve the structure, using different chains of ricin, abrin-a and trichosanthin as search models. A set of consistent solutions was further verified by R(omit) profile analysis. In addition, the spatial arrangement of the two chains of TKL-1 is identical to that of type 2 RIPs.