The effects of O₃, SO₂ and NO₂ on aspects of solute transport across the plasma membrane of R.communis var. Gibsonii cotyledons have been investigated in order to explain the observed damage resulting from plant exposure to these gases. Plasma membrane vesicles, purified by aqueous two-phase partitioning, were used to investigate the effects of Na₂SO₃ and NaNO₂ on the plasma membrane H⁺ -ATPase in vitro. Both treatments increased enzyme activity but a specific site of damage was not determined. The effects of O₃ and SO₂ on the plasma membrane H⁺ -ATPase in vivo was determined using a KI-treated microsomal fraction. Both gases increased enzyme activity but the nature of this change was unclear. A KI-treated microsomal fraction was used to determine the effects of Na₂SO₃ and NaNO₂ on the proton pumping activity of the H⁺ -ATPase in vitro. Rate of proton pumping was not affected but in some cases the magnitude of the pH gradient established was decreased. Membrane leakiness was not significantly affected. Na₂SO₃ and NaNO₂ had no effect on the rate of proton pumping by intact cotyledons but in some cases the magnitude of the pH gradient established was affected. Na₂SO₃ inhibited sucrose uptake into phase partition purified plasma membrane vesicles at high concentrations. The pH gradient across both membrane vesicles and artificial liposomes was dissipated only when Na₂SO₃ and NaNO₂ were present in the uptake medium. Na₂SO₃ did not affect the transmembrane electrical gradient. Sucrose uptake into cotyledon discs was stimulated by low levels of Na₂SO₃. NaNO₂ and high levels of Na₂SO₃ inhibited sucrose uptake.