Human mucosal microvascular endothelial cells (HMMECs) were isolated and cultured from the mucosa of nasal inferior turbinates. These cells were identified by human factor-VIII antigen and UEA-I. We also investigated alterations in intracellular calcium concentration [Ca2+]i, in HMMECs using the Ca2+-sensitive dye fura-2. Depolarization by high K+ (150 mM) induced no changes in [Ca2+]i in HMMECs, thereby indicating the lack of voltage-dependent Ca2+ channels in these cells. Extracellular ATP increased [Ca2+]i in HMMECs both in the presence and absence of extracellular Ca2+. These results suggest that ATP may induce a release of Ca2+ from intracellular stores in HMMECs. Adenosine induced no changes in [Ca2+]i in HMMECs. It is thus likely that HMMECs obtained from the nasal inferior turbinate may carry P2-purinoceptors but not P1-purinoceptors.