In African trypanosomes the requirements for glucose and its metabolism vary in different stages of the life cycle. Here we present evidence that cultured procyclic trypanosomes of Trypanosoma brucei rhodesiense uptake glucose against a concentration gradient in a time and dose-dependent manner. Moreover, glucose transport is completely inhibited by the sulphydryl inhibitor N-ethylmaleimide, suggesting the presence of a protein moiety as the carrier molecule. Comparison of glucose uptake in bloodstream and procyclic trypanosomes point to the possibility that different transporters may function in the 2 developmental stages. Glucose uptake by bloodstream trypanosomes requires Na+ ions and is inhibited by phlorizin, an inhibitor of Na(+)-dependent glucose transporters in mammalian cells. Conversely, procyclic trypanosomes transport glucose in a Na(+)-dependent manner, and transport is not affected by phlorizin. Finally, the putative procyclic glucose transporter has a higher affinity for glucose (apparent Km 23 microM) than the bloodstream carrier (apparent Km 237 microM).