The data presented here are consistent with a proton-sugar co-transport in germinated pollen of Lilium longiflorum Thunb. Optimal uptake occurs at pH 5.0. A K(m) of 1.7 to 1.8 millimolar is obtained from the initial rate of pH change induced by sucrose uptake as well as from uptake of [U-(14)C]-sucrose. The energy of activation is - 11 kilocalories mole(-1). The effect of several inhibitors and sugar competitors on [U-(14)C]sucrose and d-[U-(14)C] glucose uptake is given. The possibility of hydrolysis of sucrose prior to its transport into the pollen tube has been considered and reasons for choosing a sucrose-type uptake are presented. The possible in vivo significance of this co-transport process during pollen germination is discussed. Germinated pollen has features to recommend it as an experimental system of choice for studies of sugar uptake.