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We investigated whether the stimulation of human granulosa-lutein cells with muscarinic and nicotinic receptor agonists can cause increases in intracellular free calcium (Ca2+), using Fura-2 microfluorimetry. The addition of carbachol (a non-selective muscarinic and nicotinic receptor agonist) to cultured human granulosa-lutein cells increased intracellular free Ca2+ levels. Concentrations as low as 10 nmol/l were effective. In contrast, nicotine did not evoke elevations of intracellular free Ca2+. Basal Ca2+ levels ranged around 70–140 nmol/l and maximal, carbacholinduced peaks reached 1·1 μmol/l. The carbachol-induced Ca2+ signal was abolished after preincubation of the cells with the muscarinic receptor antagonists quinuclidinyl benzilate or atropine, but it was not affected by removal of extracellular Ca2+. Further evidence for the involvement of intracellular Ca2+ stores is provided by experiments in the absence of extracellular Ca2+. While thapsigargin (a blocker of ATP-driven Ca2+ uptake by intracellular stores) and ionomycin (an ionophore by which Ca2+ is released from intracellular stores) evoked small Ca2+ transients, cells pretreated with these agents did not respond to carbachol any more. These data suggest the presence of a functional muscarinic receptor on human granulosa-lutein cells and imply the involvement of intracellular Ca2+ stores during the cellular response. These results also suggest the participation of the nervous system, acting through muscarinic receptors, in the control of the function of human granulosa-lutein cells. Journal of Endocrinology (1992) 135, 153–159