Abstract Preincubation of yeast cells with glucose or other metabolic energy sources increased the rate of sorbose efflux 2- or 3-fold. Stimulated rates persisted for several h, decreasing slowly. They were approximately halved by including K m concentrations of highly competitive sugars such as deoxyglucose, glucose, fructose and mannose in sorbose efflux suspensions, and were greatly slowed at reduced temperatures. Inhibitors of energy metabolism blocked the rate stimulation, as did cycloheximide; added nitrogen sources increased the rate additionally. The rate of sorbose uptake was also increased, whereas that of dimethylsulfoxide, which enters the cell by simple diffusion, was not changed. Transport of arabinose and fucose also occurred at increased rates. The data indicate a change in the sorbose transport system rather than in membrane permeability. The change, apparently the synthesis of a transport system component, requires metabolic energy and involves protein synthesis.