The effect of adenosine on intracellular free calcium concentration ([Ca2+]i) was studied in human uterine myocyte. Adenosine 10(-6) M elicited a rapid followed by a maintained increase in [Ca2+]i in Fluo-3-loaded myocytes. Compared with basal [Ca2+]i level, adenosine induced a 2.6-fold increase in the absence of extracellular calcium, and a 2.4-fold increase in the presence of extracellular calcium. There was no significant difference between the two groups in the initial response. After depletion of intracellular calcium stores by repetitive caffeine (10 mM) applications, adenosine could not induce increase in [Ca2+]i. The initial rise could be induced in the absence of extracellular calcium, whereas the maintained phase after 120 s of adenosine application was dependent on the presence of extracellular calcium. The maintained phase response was 1.39- and 0.90-fold compared with basal [Ca2+]i level in the presence and absence of extracellular calcium respectively. There was significant (p < 0.01) maintenance of [Ca2+]i in the presence of extracellular calcium, which appeared to be associated with calcium influx. The data suggest that in human uterine myocytes, adenosine stimulates release of Ca2+ from intracellular stores and influx of extracellular Ca2+ through Ca2+ entry pathway.