A 2-l. bioreactor was used to culture yeast (Saccharomyces cereviasiae) and fungi (Rhizopus nigricans) with perfluorodecalin (/) as O-2 vector and/or with conventional aeration by bubbling. / was superior as oxygenator, with vol. mass-transfer coeffs. k(L)a = 0.38-0.152 min(-1) as detd. by the dynamic method. With the yeast culture showed a shorter lag-phase and a 110% increase in biomass efficiency. In the fungus culture, diffusion controlled the 02 transport in cell-pellets and / did not improve the aeration.