Abstract: Researchers test the effects of Norstictic acid, secondary metabolite of the lichen Buellia zahlbruckneri, on the growth of murine SV40 transformed lymphoid carcinoma cells in vitro. Researchers find that Norstictic acid is a potent inhibitor of growth. Researchers, also find that Norstictic acid increases sensitivity of cells to radiation and this effect is significant at a radiation intensity lower than the standard intensity of cancer radiotherapy. On the basis of this study, Norstictic acid shows promise for combined-modality cancer treatment.