The effect of increased total pressure and partial pressures of oxygen and carbon dioxide on the growth of Pseudomonas fluorescens was investigated in an airlift reactor. In batch cultivations bacterial growth was completely inhibited with air at 8 bars total pressure. The same effect was observed with aeration by pure oxygen at 1.15 bars. Carbon dioxide partial pressure did not show inhibitory effects. Continuous experiments confirm the assumption that growth inhibition at higher total pressure is caused by the increase in oxygen partial pressure. Incubation of P. fluorescens at higher oxygen partial pressure led to an increase of bacterial productivity during subsequent continuous cultivation at ambient pressure (1 bar) with air. Maximum productivity was increased by about 75% after aeration with pure oxygen. This effect is probably the result of metabolic adaption of the bacterial cells to high oxygen partial pressure.