Supplementation of cattle diets with a blend of oils rich in omega-3 polyunsaturated fatty acids (ω-3 PUFA) and linoleic acid have a synergistic effect on the accumulation of ruminal and tissue concentrations of vaccenic acid (VA), the main substrate for ∆-9 desaturase catalysed de novo tissue synthesis of the cis 9, trans 11 isomer of conjugated linoleic acid (CLA). This dietary strategy translates into increases in milk concentrations of CLA in dairy cows, however, CLA concentrations in the muscle of beef animals have not always been increased (Kenny et al., 2007). Studies with in-vitro mammary cell lines (Keating et al., 2006) and mice (Ntambi et al., 1999) suggest that ω-3 PUFA may inhibit expression of ∆-9 desaturase. Furthermore, the promoter regions of the bovine ∆-9 desaturase gene have been shown to contain a conserved PUFA response region (Keating et al., 2005) and this has been suggested as a mechanism through which ω-3 PUFA may modulate ∆-9 desaturase expression in bovine muscle. Currently there is no evidence to support this hypothesis. The objective of this study, therefore, was to determine the influence of ω-3 PUFA dietary supplementation on the expression of ∆-9 desaturase gene in bovine muscle.