Menhaden oil was interesterified with CLA in a packed-bed reactor containing an immobilized lipase from Mucor miehei (L9) as the biocatalyst. Process optimization was studied using a sequence of 2(2) x 3 factorial designs involving the mole ratio of reactants, the reaction temperature, and the space-time of the reactor as experimental parameters. Three different responses-percentage of incorporation of CLA, level of n-3 residues remaining, and conversion of CLA-were considered as objective functions. The parameters studied showed opposite effects for incorporation of CLA and the retention level of n-3 residues. A desirability function was constructed to describe a desirable balance of the conflicting response variables. Optimal conditions correspond to a molar ratio of CLA to fish oil of 0.8 to 1, a temperature of 60degreesC, and a space-time of 3 h.