This study investigated a potential mechanism of action underlying the anticancer activity of conjugated lmoleic acid (CLA), referring to a mixture of positional and geometric conjugated isomers of lmoleic acid Ras, an oncogene necessary for normal cell function, when mutated results in uncontrolled cell proliferation and consequently tumour formation Western blot analysis suggested that c9, ill and flO, cl2 CLA isomers inhibit (P<0 05) expression and activation of mutated ras compared with ethanol control in SW480 cells, a numan colon cancer cell line. Lmoleic acid stimulated cell growth, however it reduced ras expression, suggestmg that events downstream of ras may be more critical targets for modulating growth by these fatty acids. A second objective was to investigate the cytotoxic effect of CLA-rich oils produced by thefermentation of lmoleic acid by selected CLA-producmg strains Lmoleic acid-nch oil fermented by B breve NCFB 2258 reduced growth of SW480 cells in a time dependant manner at a concentration of 84 \ig fat/ml This oil contained 20 \ig c9, t\ 1 CLA/ml. When pure fatty acids were combmed to mimic the fatty acid profiles of the microbially fermented oils, the growth inhibitory effect observed was only partly attributable to the CLA content of the oil. This study also examined a nutritional approach to the enrichment of CLA m milk fat by dietary supplementation of pre-selected cows on pasture with full fat rapeseeds Surprisingly, there was no significant effect on milk fat c9, /II CLA due to rapeseed supplementation. In addition, elaidic acid, a fatty acid not previously demonstrated to be influenced by rapeseed supplementation, increased significantly in the milk of cows on the supplemented diet. These unexpected results may be attributed to excessive ramfall throughout the period of the trial affecting pasture quality and possibly an altered biohydrogenation process.