Ribosome-inactivating proteins have been isolated from Trichosanthes kirilowii root tubers and seeds, including trichosanthin, karasurin and T 33 from root tubers and trichosanthrip, trichokirin, alpha-kirilowin, beta-kirilowin and trichoanguin from seeds. The aforementioned proteins show structural and functional similarities. Among them trichosanthin is the best known and most intensely studied. Trichosanthin manifests anticancer activity in vitro and in tumor bearing mice against a variety of cancers/cancer cell lines. It also exhibits anti-HIV-1 and anti-HSV-1 activities. Trichosanthin has been found to be useful for treatment of cesarean scar pregnancies and ectopic pregnancy, and for preventing acute rejection of major histocompatibility complex-mismatched mouse skin allograft. Trichosanthin selectively lesions some neurons and thus can be used in neuroscience research.