The serotonin1A (5-HT1A) receptors are important members of the superfamily of seven transmembrane domain G-protein coupled receptors. They appear to be involved in various behavioral, cognitive and developmental functions. Mammalian cells in culture heterologously expressing membrane receptors represent convenient systems to address problems in receptor biology. We report here the pharmacological characterization of one of the first isolated clones of CHO cells stably expressing the human 5-HT1A receptor using the selective agonist 8-OH-DPAT and antagonist p-MPPF. In addition, we demonstrate that agonist and antagonist binding to the receptor exhibit differential sensitivity to the non-hydrolyzable GTP analogue, GTP-gamma-S, as was observed earlier with the native receptor from bovine hippocampus. These results show that the human 5-HT1A receptor expressed in CHO cells displays characteristic features found in the native receptor isolated from bovine hippocampus and promises to be a potentially useful system for future studies of the receptor.