Conjugated Linoleic Acid (CLA) is a mixture of isomers of linoleic acid implicated with numerous health promoting properties. These include anti-carcinogenicity (cis -9, trans -11 isomer), anti-atherogenicity and increasing the lean:fat ratio (trans -10, cis -12 isomer). CLA is produced naturally by all ruminant animals through the incomplete biohydrogenation of linoleic acid within the rumen. Alternatively, it can be made endogenously by stearoyl coenzyme A desaturase (SCD) from vaccenic acid (VA) (Griinari et al, 2000). It has been well documented that cows fed on a grass diet produce more cis -9, trans -11 in milk than those fed on a concentrate based regime (Kelly et al, 1998) but to date, little work would appear to have been undertaken to determine if this is the case with sheep tissues. In the present study, a grass based diet was compared with a concentrate diet in order to determine whether the CLA content of adipose tissue differed and if so, which isomer and what mechanisms may be involved.