Walker 256 carcinosarcoma cells (1 x lo4) were injected into the right thigh muscle of Sprague-Dawley rats (125 g) consuming isoenergetic (200 g fat/kg) diets containing 20, 100 and 200 g maize oil/kg and 180, 100 or 0 g hydrogenated lardfkg respectively. Ten rats from each dietary regimen were killed every 4th day. Tumours grew rapidly from day 0 to day 8 post-transplant regardless of dietary regimen. However, after 8 d more tumours regressed and there were fewer deaths in animals fed on 200 g maize oil/kg compared with animals fed on 20 or 100 g maize oil/kg. Linoleic acid (LA) levels were higher in phospholipids (PL) of growing tumours than in regressing tumours whereas arachidonic acid levels in PL were lower in growing tumours indicating a possible alteration in the desaturation and elongation of LA. Serum prostaglandin E, levels were slightly lower in rats with regressing tumours than in rats with growing tumours.Linoleic acid : Cancer: Lipids: Walker 256 carcinosarcoma : Growth ~.