The effect of feeding n-3 PUFA on the fatty acid composition of muscle, adipose tissue and liver of lambs was investigated. Groups of eight ram lambs per breed, Suffolk X Lleyn (24 kg live weight) and Scottish Blackface (18 kg live weight), were each fed one of six diets containing one of three fat sources (50 g fatty acids/kg DM; Megalac(R) (calcium soap of palm fatty acid distillate; Volac Ltd, Royston, Herts., UK) and formaldehyde-treated whole linseed (Trouw Nutrition UK, Northwich, Ches., UK) either alone or with fish oil (1:1, w/w) and either 100 or 500 mg alpha-tocopheryl acetate/kg DM. Feed was offered ad libitum until slaughter at approximately half breed mature live weight. The type of dietary fat had no effect on intake, growth rate or feed conversion ratio. The 3.0-fold higher concentration of 18: 3n-3 in the linseed compared with the Megalac(R) diet approximately doubled (P<0.001) the concentration in the neutral and polar lipid fractions of musculus semimembranosus and liver, and in adipose tissue it increased 2.5-fold. Feeding protected linseed also increased (P< 0.001) concentrations of 20: 5n-3 and 22: 5n-3 in muscle polar lipids and both lipid fractions of liver. The linseed-fish oil raised the 20: 5n-3 concentrations above those for the linseed diet and also increased 22: 6n-3. Scottish Blackface lambs had lower concentrations of 18: 3n-3 in all lipids compared with Suffolk x Lleyn lambs, but more 20: 5n-3 in the polar lipids of muscle and liver. High levels of dietary vitamin E were associated with small decreases in the concentration of monounsaturated fatty acids and increases in PUFA. Linseed raised the PUFA: saturated fatty acid ratios in liver and adipose tissue but not in muscle, and improved the n-6:n-3 fatty acid ratio, as did the linseed-fish oil. Different combinations of dietary fatty acids and better protection against rumen biohydrogenation are required to improve muscle PUFA: saturated fatty acids ratios.