It is commonly supposed that dioxygen (O-2) transport through biomembranes is ensured by the high permeability of a lipid bilayer in which O-2 diffusion mobility is close to that in water. However, the fact that microviscosity of lipid membranes is higher than that of water by two to three orders of magnitude speaks against this concept. Therefore, in this work we investigated the influence of surface lipid monolayers on oxygen diffusion flow directed from air to aqueous phase. We show that for lipid monolayers, the O-2 permeability coefficients are within the range of 10(-4) to 10(-5) m/s. These values are three to four orders of magnitude lower than has been previously thought, indicating that lipid membranes constitute a considerable barrier to O-2 diffusion. From this, we suggest that membranes of aerobic organisms contain O-2 channels to ensure the high-volume transmembrane O-2 flows. (C) 2004 Elsevier Inc. All rights reserved.