Repetitive transient increases in intracellular calcium were recorded in single cultured human myometrial cells exposed continuously to oxytocin (1 pM-1 nM). Each transient was preceded by a pacemaker-like gradual increase in baseline [Ca2+]i. Removal of extracellular Ca2+ reversibly stopped the transients although small fluctuations in [Ca2+]i were observed in seven out of eleven cells studied. In a proportion of cells (1-2%) repetitive Ca2+ transients were observed in the absence of exogenous oxytocin. The pattern of activity was similar to that seen in cells exposed to oxytocin. These spontaneous elevations in [Ca2+]i were reversibly inhibited by removing extracellular calcium. These experiments demonstrate for the first time repetitive agonist-induced and spontaneous transient increases in [Ca2+]i in single cultured human myometrial cells.