Under High Aspect Ratio Vessel (HARV) bioreactor culture conditions designed to simulate the microgravity of orbital space flight, insect tissue culture cells infected with a baculovirus expression vector produced a human glycoprotein with tri- and tetra-antennary complex N-linked oligosaccharides containing terminal sialic acid residues. The oligosaccharide structures were similar to those produced in human placental cells. Insect cells cultured in T-flasks only performed incomplete oligosaccharide processing. The mechanism of HARV-mediated changes in the eukaryotic N-linked glycosylation pathway was investigated and could be mimicked under T-flask growth conditions with the addition of N-acetylmannosamine to the culture medium. The significance of these investigations is discussed with respect to the production of recombinant therapeutic glycoproteins, insect physiology, and orbital space flight.