High cell density cultivation of Pichia pastoris has to cope with several technical limitations, most importantly the transfer of oxygen. By applying hypoxic conditions to chemostat cultivations of P. pastoris expressing an antibody Fab fragment under the GAP promoter, a 2.5-fold increase of the specific productivity q(P) at low oxygen supply was observed. At the same time the biomass decreased and ethanol was produced, indicating a shift from oxidative to oxidofermentative conditions. Based on these results we designed a feedback control for enhanced productivity in fed batch processes, where the concentration of ethanol in the culture was kept constant at approximately 1.0% (w(-1)) by a regulated addition of feed medium. This strategy was tested successfully with three different protein producing strains, leading to a three- to sixfold increase of the qp and threefold reduced fed batch times. Taken together the volumetric productivity Q(P) increased 2.3-fold.