In this study, we determined the expression patterns of the 5-HT7 receptor isoforms at the mRNA level in the rat jejunum and other regions of the rat digestive tract using reverse transcriptase-PCR. In control studies using the rat thalamus, we detected all three known isoforms of the rat 5-HT7 receptor, 5-HT7(a), 5-HT7(b) and 5-HT7(c). In addition, we also detected in the thalamus a new PCR product that we provisionally name 5-HT7(e). All four isoforms of the 5-HT7 receptor were present throughout the rat digestive tract. However, the spatial distribution and levels of expression of the different isoforms varied between regions of the rat digestive tract. All three known isoforms and the provisional isoform were found in the jejunum, ileum, stomach fundus, oesophagus and colon. The level of expression of the isoforms varied with all four being most consistently found in the ileum. The 5-HT7(a) receptor isoform was predominantly expressed in the rat digestive tissue and 5-HT7(b,, 5-HT7(c) and 5-HT7(e) were only sometimes expressed but always accompanying the receptor isoform 5-HT7(a).