An improved system for large scale production of glycoproteins in cell culture is provided. In accordance with the present invention, cells expressing a glycoprotein are grown in media that contain manganese at a concentration of between approximately 10 and 600 nM. The use of such a system allows production of a glycoprotein with an increased glycosylation pattern and/or a glycosylation pattern that more accurately reflects the glycosylation pattern of the naturally occurring glycoprotein. A glycoprotein expressed in accordance with the present invention may be advantageously used in the preparation of pharmaceutical compositions.