Human antithrombin In variant (AT III) production from recombinant BHK cells was investigated in a spinner flask fed-batch culture associated with an on-line HPLC system. Six experiments were carried out using three set points for the glucose concentration (0.5, 2.0, and 3.0 g/l) and two set points for the glutamine concentration (0.2 and 0.6 g/l). The highest concentration of AT III, which was obtained in the experiment with 3.0 g/l glucose and 0.2 g/l glutamine, was about two times higher than the lowest concentration obtained. The monosaccharide content of the AT III produced was almost the same in all the experiments, though the amount of sialic acid detected in the AT III produced in two of the experiments with 3.0 g/l of glucose was a little on the low side.