Avène spa water (ASW) inhibits the histamine release induced in mast cells by substance P; the inhibition is reversed by EDTA and by EGTA. Calcium and magnesium ions, the major cations present in ASW, were experimented in simple saline solutions in the presence of various counter-ions. Only calcium salts inhibited the peptidergic stimulation, with different potencies ruled by the nature of the counter-anion (HCO3- > Cl- > SO4(2)). On a Ca2+ concentration basis, ASW was, however, more inhibitory, suggesting that other compounds present in ASW potentiate the effect of calcium.