For a mass-transfer-limited system, it was demonstrated that the volumetric ethene transfer coefficient (k(1) alpha) from gas to water could be enhanced by dispersing adequate amounts of a water-immiscible organic liquid, namely the perfluorocarbon FC40, in the aqueous phase. When 26% (v/v) FC40 was dispersed in a culture of Mycobacterium parafortuitum an enhancement of k(1) alpha, calculated on a total liquid volume basis, of 1.8 times was found. Steady-state experiments in the absence of microorganisms, however, showed a 1.2-fold enhancement of k(1) alpha at 18.5% (v/v) FC40. At all FC40 volume fractions tested, enhancement factors with cells were higher than enhancements without cells; apparently the microorganisms or their excretion products affected the interfacial areas or characteristic phase dimensions.