Objective: Although pharmacological studies have indicated that serotonin (5-HT)-evoked contraction of the human coronary artery is mediated by 5-HT₁-like and 5-HT₂ receptors, the gene expression of 5-HT receptors is still unclear. We examined mRNA expression of 5-HT₁ and 5-HT₂ receptor subtypes in human coronary arteries. Methods: Total RNA was extracted from human coronary arteries of 14 patients at autopsy by the guanidine method. Reverse transcription-polymerase chain reaction (RT–PCR) and ribonuclease protection assays were performed to identify 5-HT₁ and 5-HT₂ receptor mRNA expression in human coronary artery. Results: By RT–PCR, 5-HT_1B, 5-HT_2A and 5-HT_2B mRNAs were detected in all of the 14 patients. 5-HT_1A, 5-HT_1D, and 5-HT_1E mRNAs were detected in only some patients. However, neither 5-HT_1F mRNA nor 5-HT_2C mRNA was detected in any patient. By ribonuclease protection assay, 5-HT_1B and 5-HT_2A signals were detected in all patients examined, but neither 5-HT_1A, 5-HT_1D nor 5-HT_2B signal was detected in any patient. Conclusions: Of 5-HT_1/2 receptor subtypes, 5-HT_1B and 5-HT_2A receptor mRNAs were predominantly expressed in human coronary arteries. Our finding provides molecular evidence that the 5-HT_1B receptor may be the 5-HT₁-like receptor which mediates constriction of human coronary arteries.