We examined the expression of human cyclooxygenase-1 (COX-1) in Drososphila melanogaster S2 (S2) cells transformed with cDNAs encoding beta 1,4-galactosyltransferase (GalT) and Gal beta 1,4-GlcNAc alpha 2,6-sialyltransferase (ST). Southern blot analysis indicated that multiple copies of the glycosyltransferases genes were integrated into the S2 cell genome. A lectin blot analysis also indicated that recombinant COX-1 from S2COX-1/GalT-ST cells contained the glycan residues of beta 1,4-linked galactose and alpha 2,6-linked sialic acid. The specific peroxidase activity of recombinant sialylated COX-1 from S2COX-1/GalT-ST cells was 41,250 U mg(-1), indicating an increase of approximately 22% compared with a non-sialylated control (33,850 U mg(-1)) from S2COX-1 cells.