Abstract. In cystic fibrosis, the mutation of the CFTR protein causes reduced transepithelial Cl secretion. As recently proposed, beside its role of Cl channel, CFTR may regulate the activity of other channels such as a Ca2+-activated Cl channel. Using a calcium imaging system, we show, in adenovirus-CFTR infected Chinese Hamster Ovary (CHO) cell monolayers, that CFTR can act as a regulator of intracellular [Ca2+]i ([Ca2+]i), involving purino-receptors. Apical exposure to ATP or UTP produced an increase in ([Ca2+]i in noninfected CHO cell monolayers (CHO-WT), in CHO monolayers infected with an adenovirus-CFTR (CHO-CFTR) or infected with an adenovirus-LacZ (CHO-LacZ). The transient [Ca2+]i increase produced by ATP or UTP could be mimicked by activation of CFTR with forskolin (20 m) in CHO-CFTR confluent monolayers. However, forskolin had no significant effect on [Ca2+]i in noninfected CHO-WT or in CHO-LacZ cells. Pretreatment with purino-receptor antagonists such as suramin (100 m) or reactive blue-2. (100 m), and with hexokinase (0.28 U/mg) inhibited the [Ca2+]i response to forskolin in CHO-CFTR infected cells. Taken together, our experiments provide evidence for purino-receptor activation by ATP released from the cell and regulation of [Ca2+]i by CFTR in CHO epithelial cell membranes.