The phosphoglycerate kinase (PGK)-encoding genes of Trypanosoma brucei are transcribed in a polycistronic fashion, but the mRNAs encoding the three PGK isozymes show differing developmental regulation. We demonstrate here that the 3'-untranslated regions of the major cytoplasmic and glycosomal PGK isozymes are capable of conferring the anticipated types of regulation on a transfected reporter gene.