The secretion of nitric oxide (NO) was stimulated by the addition of ATP or ADP, but not by AMP or adenosine, in cultured bovine aorta endothelial cells. Inhibitors of ecto-ATPase, NaN3 and Ap5A, significantly inhibited the stimulation, while an inhibitor of P2Y-purinoceptor and ecto-ATPase, RB2, completely suppressed it. A non-hydrolyzable ATP analogue, AMP-PNP, stimulated NO release; the stimulation was completely suppressed by RB2 but not by NaN3 and Ap5A. Therefore, only P2Y-purinoceptor was involved in the stimulation by AMP-PNP, while both ecto-ATPase and P2Y-purinoceptor were involved in the stimulation by ATP and ADP. It is not clear whether the stimulation is dependent on the dephosphorylation activity of ecto-ATPase or not, but the enzyme appears to act as an ATP and ADP receptor for signal transduction through adenine nucleotides.