The inhibitory peptide hormone somatostatin and its receptors (sst1-sst5) regulate many physiological functions in the gastrointestinal tract. In an attempt to correlate the various effects of somatostatin in gastrointestinal physiology to individual sst subtypes sst1-sst5, mRNAs have been localized by semiquantitative reverse transcription polymerase chain reaction amplification and in situ hybridization of sst1 and sst3 in the rat alimentary tract. sst1-sst4 mRNAs were found throughout the gastrointestinal tract, sst1 mRNA being more abundant than sst2 and much more abundant than sst3 and sst4 mRNAs. sst5 transcripts were at the detection threshold. sst1 and sst3 mRNAs are present in enterocytes and enteric neurons suggesting a role of these subtypes in the somatostatin-mediated inhibition of acetylcholine release from myenteric neurons and of secretomotor neuron activity in the submucous plexus. The presence of sst3 mRNA in smooth muscle cells points to an additional role of this receptor in regulating gut motility. Copyright 1999 Harcourt Publishers Ltd.