A nonionic surfactant, Pluronic F-68, was used to investigate mass transfer characteristics of a fermentation medium in a 11 bench-top bioreactor. At low flow rate (0.08 vvm), k(L)a did not change significantly with increasing agitation speed. In all air flow rates studied, pluronic caused a remarkable reduction in k(L)a. When an oxygen carrier such as perfluorocarbon (PFC) was added to the medium, k(L)a increased with increasing PFC concentration. Moreover, PFC emulsified with pluronic F-68 resulted in a significant increase in k(L)a values. The inclusion of 4 g l(-1) pluronic in yeast fermentation medium resulted in a longer lag phase, while the final biomass concentration was almost unaffected.