Menhaden oil, a rich source of n-3 fatty acids, was interesterified with conjugated linoleic acid (CLA) in a reaction medium composed solely of substrates and either free or immobilized commercial lipase preparations. Of five lipases tested, an immobilized preparation from Mucor miehei provided the fastest rate of incorporation of CLA into fish oil acylglycerols; however, and as observed with most of the lipases utilized, a significant proportion of the n-3 fatty acid residues were liberated in the process. A soluble lipase from Candida rugosa converted free CLA to acylglycerol residues while leaving the n-3 fatty acid residues virtually untouched. Even though the reaction rate was slower for this enzyme than for the other four lipase preparations, the specificity of the free C. rugosa lipase gives it the greatest potential for commercial use in preparing fish oils enriched in CLA residues but still retaining their original n-3 fatty acid residues.