6-O-Eicosapentaenoyl L-ascorbate (EPA-AsA) was synthesized through condensation of eicosapentaenoic acid (EPA) and L-ascorbic acid in acetone using immobilized lipase from Candida antarctica, Chirazyme L-2. The maximum yield of 47% was attained with 620 mmol EPA and 0.125 mmol L-ascorbic acid in 2.5 ml acetone dehydrated by molecular sieves at 55 degrees C. More than 80% of the EPA-AsA remained in the unoxidized state at 65 degrees C and at 0% relative humidity although the unmodified EPA was completely oxidized within 3 h under these conditions.