A Trypanosoma brucei gene encoding 6-phosphogluconate dehydrogenase (6-PGDH) (EC 1.1.1.44) was identified and cloned by functional complementation of Escherichia coli gnd mutants with genomic trypanosome DNA. The T. brucei gnd gene is present as a single copy. In Northern blot experiments a probe derived from the gene hybridises to 2 transcripts (2.9 kb and 3.1 kb) which are found in both bloodstream and procyclic form organisms; the larger transcript is more abundant in bloodstream form organisms. The derived amino acid sequence of the protein is 479 amino acids in length, with a molecular weight of 52,000. It is homologous to 6-PGDHs from bacterial and mammalian sources, but diverges significantly from these other enzymes.