5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a new analogue of FAA developed in the ACSRC, showed greater activity and 12-fold higher dose-potency than FAA in murine tumour models (Rewcastle et al, 1991) and appeared to overcome the species difference in in vitro TNF production (Ching et al, 1994; Philpott et al, 1997). This evidence concerns the gene TNF and neoplasm.