We have studied the effect of ATP on Ca 2+ uptake in intestinal brush border membrane vesicles (BBMVs) of the teleost tilapia ( Oreochromis mossambicus ). ATP stimulated Ca 2+ uptake 12-fold over the control, with a linear time course. Ionomycin and detergent treatment did not reduce BBMVs' Ca 2+ content, indicating the binding of Ca 2+ to a membrane component. A rank order of ATP > ADP > AMP was established for the stimulation of Ca 2+ uptake. Adenosine, vanadate, adenosine 5ƀ-[α,β-methylene]triphosphate (a P 2X purinoceptor agonist) and adenosine 5ƀ-[γ-thio]triphosphate (a P-type ATPase inhibitor) were without effect. 2-Methylthioadenosine 5ƀ-triphosphate, a P 2Y purinoceptor agonist, mimicked the stimulation by ATP. As judged from a kinetic comparison, ATP hydrolysis and the stimulation by ATP of Ca 2+ uptake were not compatible. The P 2 purinoceptor antagonist suramin and the P 2Y purinoceptor antagonist Reactive Blue-2 inhibited the Ca 2+ uptake stimulated by 1 mM ATP (IC 50 0.17 mM and 58 Ɓ M respectively). We conclude that ATP-stimulated Ca 2+ uptake in tilapia intestine is dissociated from ATPase activity and is mediated through a P 2 purinoceptor.