Red blood cells (RBCs) exchange their entire intracellular water about one hundred times per second. This is due to the remarkable metabolic rate of these cells with plenty of transporter activities across the membrane besides substantial gas exchange reactions of O₂ and CO₂. It had long been believed that gases enter and leave the cells only by simple diffusion through the membrane lipids. This axiom needed to be reconsidered after the expression of the water channel AQP1 in Xenopus oocytes gave evidence for the functionality of AQP1 as a gas pore (Boron & coworkers, 1998). The same year the HCO₃^--Cl^-exchange protein AE1 was classified as a potential CO₂ channel (Forster, Gros & coworkers). The hypothesis both proteins may serve as gas transfer routes within one membrane was tested on CO₂ transport in RBC ghosts loaded with the proton sensitive dye BCECF. Any specific acidification was restricted to the intracellular space and required the catalytic activity of CA. Rates of acidification under functional inhibition of AQP1 by pCMBS or HgCl₂ revealed a possible contribution of the cytoskeleton. This was supported by results in the presence of the AE1 inhibitors DIDS or oxonol which totally suppressed fast acidification as well as rapid volume changes. In conclusion, AE1 and AQP1 may act together in a functional complex allowing high affinity gas transfer and a