Members of the Rab family of low molecular weight GTP-binding (LMWG) proteins regulate vesicular transport; distinct Rab proteins are located in specific vesicular compartments within the exocytotic and endocytotic pathway. Pancreatic zymogen granules possess multiple LMWG. Rab 3A, however, which has been suggested to regulate exocytosis of synaptic vesicles, is not present in rat pancreatic acinar cells or on zymogen granules (BBRC 1994,269:542-548). To look for homologues of Rab 3A we have screened a rat pancreatic cDNA library using Rab 3A as a probe. We now report the cDNA and deduced amino acid sequence of a new member of the Rab protein family. Rab 26 is a 190 AA protein with a predicted molecular mass of 21,459 Dalton. It is expressed in pancreas, kidney, brain, submandibular gland, and lung. It is most closely related to Rab 8. There is also close homology to Rab 15, Sec4 and Rab 3.