A CHO cell line producing t-PA was cultured using glutamate and glucose or galactose to decrease the formation of metabolic end-products and therefore improving the process. In batch cultures using glutamate (6mM) with glucose at two different levels (5 and 20mM) or with glucose and galactose (5 and 20mM, respectively) a remarkable difference in cell culture parameters was evidenced. For 20mM glucose, a usual cell pattern was observed with lactate built-up in the medium. For 5mM glucose, cell growth was arrested due to glucose depletion and only a limited use of the excreted lactate could be observed, not supporting cell growth sufficiently. However, when glucose 5mM and galactose 20mM were used together, cells consumed the glucose first and, interestingly, in a second phase they continued growing on galactose with the simultaneous consumption of the endogenous lactate. Under these conditions, cell growth was even improved with respect to growth on 20mM glucose, used as a control. This metabolic behavior is further investigated by using metabolic flux analysis, suggesting that the lactate produced is not used in the oxidative metabolism through the TCA cycle. Metabolic fate of the lactate consumed is discussed.