Oridonin (Ori) is an active principle isolated from Rabdosia rubescens. The cytotoxic effect of the combination of Ori and cisplatin was tested by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] colorimetric assay. IC50 of cisplatin to cultured S180 cells in 24 h was 9.38 micrograms.ml-1. When the cells were treated with cisplatin plus Ori 0.5 and 1 microgram.ml-1, the IC50 were 1/3.4 and 1/6.7, respectively, of that with cisplatin alone. Modified alkaline elution was used to detect the DNA interstrand cross-link and DNA-protein cross-link in S180 cells induced by the 2 drugs. A greater amount of DNA cross-link was detected when the cells were treated with cisplatin plus Ori than with cisplatin alone (P < 0.05). After lysis by proteinase K, a reduction in DNA cross-link was seen, which suggested that the drugs could produce both kinds of DNA cross-link.