Abstract: Leonurus hereterophyllus Sweet is a traditional Chinese herbal medicine used to treatmenstrual disturbances in woman. A new labclane diterpene, prehispanolone LC-5504, namely 9α,13R, 15,16-diepoxy-labclane- 14-en- 7- one, had been isolated. The authors studied the synergism oflabdane diterpene,prehispanolone LC-5504 and Con A and LPS on T cells and B cells proliferation ofBALB/c female mouses in vitro. They showed that(1) proliferation of T cells was demonstrated by ad-ministration of LC-5504 of various concentrations together with Con A. This proliferation was 5～8times stronger than that observed when Con A was used alone. Such effect on T cells was not observedwhen LC-5504 was used alone. (2) Proliferation of B cells was not observed whether LC-5504 wasused alone or together with LPS.