The human (h) TXA2 receptor (TP), a G protein-coupled receptor, exists as two isoforms, TPα and TPβ, which arise by alternative mRNA splicing and differ exclusively in their carboxyl terminal cytoplasmic regions. In this study, a reverse transcriptase - polymerase chain reaction (RT-PCR) based strategy was developed to examine the expression of the TPs in tissues of physiologic relevance to TXA2. Although most of the 17 different cell / tissue types examined expressed both TP isoforms, the liver hepatoblastoma HepG2 cell line was found to exclusively express TPα mRNA. In most cell types, TPα mRNA predominated over TPβ mRNA. Moreover, although the levels of TPα mRNA expression were similar in most of the cell / tissue types examined, extensive differences in the levels of TPβ mRNA were observed. Consequently, the relative expression of TPα : TPβ mRNA varied considerably due to extensive differences in TPβ mRNA expression. Most strikingly, primary HUVEC’s were found to express: (i) low levels of TPβ and (ii) approximately 6- fold greater levels of TPα than TPβ . These data were confirmed in the spontaneously transformed HUVEC derived ECV304 cell line. Expression of TP mRNAs in the various tissue / cells correlated with protein expression, as assessed by radioligand binding using the selective TP antagonist [3H] SQ29,548.