A novel antitumor protein, designated RE26, with anti-lymphoma activity was purified from a Tris-HCl buffer extract of Rozites emodensis (Berk.) Moser by three successive steps of ion exchange chromatography. SDS-PAGE and gel filtration chromatography revealed that RE26 is a monomeric protein of 26 kDa, and isoelectrofocusing assay indicated its isoelectric point of 4.3-4.4. RE26 has high stability over a wide pH range (pH 3-11) but is sensitive to temperature and only stable under 40 degrees C. Partial amino acid sequences of two RE26 peptide fragments were determined by Edman degradation as GLEEEETLLLLFFPP and GTEQE. The half-maximal inhibitory concentration (IC50) of RE26 against tested lymphoma cell lines was around 4 mu g/ml. In vitro experiments showed that RE26 could specifically bind to lymphoma cells; activate the caspases, including caspases 3, 8, and 9 in host cells; and induce apoptosis. Experiments in nude mice indicated local RE26 injection adjacent to tumor site could inhibit lymphoma formation.