The replacement of glucose by mannose as a means to improve recombinant protein productivity was studied for the first time in continuous cultures of Chinese hamster ovary (CHO) cells producing human recombinant tissue plasminogen activator (t-PA). Steady-state operation at two hexose levels in the inlet (2.5 and 10. mM) allowed comparing the effect of sugar type and concentration on cell metabolism and t-PA production independently of changes in specific growth rates produced by different culture conditions. An increase in biomass concentration (15-20%) was observed when using mannose instead of glucose. Moreover, specific hexose consumption rates were 20-25% lower in mannose cultures whereas specific production rates of lactate, an undesirable by-product, were 25-35% lower than in glucose control cultures. The volumetric productivity of t-PA increased up to 30% in 10. mM mannose cultures, without affecting the sialylation levels of the protein. This increase is manly explained by the higher cell concentration, and represents a substantial improvement in the t-PA production process using glucose. Under this condition, the oxygen uptake rate and the specific oxygen consumption rate, both estimated by a stoichiometric analysis, were about 10% and 25% lower in mannose cultures, respectively. These differences lead to significant differences at larger scales, as it was estimated by simulating cell cultures at different bioreactor sizes (5-5000. L). By assuming a set of regular operating conditions in this kind of process, it was determined that mannose-based cultures could allow culturing CHO cells up to 3000. L compared to only 80. L in glucose cultures at the same conditions. These facts indicate that mannose cultures may have a significant advantage over glucose cultures not only in terms of volumetric productivity of the recombinant protein but also for their potential application in large-scale productive processes.