Metabolic engineering of cell cycle regulation addresses important biotechnological problems about serum removal from animal cell culture systems. Chinese hamster ovary cells stimulated to grow by fetal calf serum, insulin, or basic fibroblast growth factor were studied by two-dimensional electrophoresis (2DE) and the resulting protein expression patterns were analyzed. Detailed 2DE protocols are provided and at least 24 gene products are identified which may play an important role in growth factor signaling. Moreover, a correlation between the expression of three proteins (cyclin D1, cyclin E, and E2F-1) and mitogenic strength was found.