Small GTP-binding proteins have been implicated in the regulation of many dynamic cellular processes. The carboxyl termini of parietal cell small GTP-binding proteins were cloned using a 3'-rapid amplification of cDNA ends (RACE) technique with a degenerate oligonucleotide primer based on the WDTAGQE consensus GTP-binding sequence. Six out of 53 clones demonstrated a novel Rab sequence, now designated Rab25. The complete sequence was obtained using 3'-RACE and revealed a deduced amino acid sequence having 63% identity with Rab11. The deduced amino acid sequence demonstrated a carboxyl-terminal CCQNI and also a novel GTP-binding site sequence of WDTAGLE. Nevertheless, recombinant Rab25 was able to bind GTP on blot. A major 1.2 kilobase Rab25 message was detected throughout the gastrointestinal mucosa and in lung and kidney tissue. No message was detected in brain, heart, liver, or skeletal muscle. In gastric tissue, Rab25 was absent in the bowel wall; among mucosal cells, it was highly enriched in parietal cells compared to chief cells. Rab25 mRNA was also detected in several colon carcinoma lines including LIM1215 and HT-29. The results indicate that Rab25 represents a novel member of the Rab family with an epithelial distribution.