Inoculation of wheat seedings withAzospirillum brasilenseCd increased proton efflux from the roots. Inoculation of seeds or young seedlings using bacterial cultures at the logarithmic phase of growth caused the strongest proton extrusion. The increased effect lasted up to 20 h. No difference was detected between inoculated and noninoculated plants 20 h after inoculation. Both inoculated and noninoculated plants decreased the final pH of the nutrient solution to 3.2 and had an average proton extrusion of 4.3 μmol H+ ∙ (g fresh weight)−1∙h−1.Azospirillum brasilenseCd inoculation of wheat roots in which proton efflux was inhibited by the addition of either nitrate, dicyclohexylcarbodiimide, or orthovanadate resulted in partial recovery of proton efflux activity in these roots. Inoculation of wheat seedlings also changed the regular pattern of root proton efflux over prolonged periods of time. It is suggested thatA.brasilenseCd inoculation influenced membrane activity and subsequent proton efflux in roots of wheat seedlings.Key words:Azospirillum, plant–bacteria interaction, proton efflux, rhizosphere bacteria,Triticum aestivum, wh