The biological activity of Avène water from two different springs ('Sainte Odile' and 'Val d'Orb') was studied in vitro on rat peritoneal mast cell activation. A dilution-dependent inhibition of both histamine and prostaglandin D2 antigen-induced release was observed when cells were preincubated with both Avène spring waters. They also inhibited histamine release triggered by substance P. The ability of Avène water to inhibit mast cell activation in vitro may be related with its antiallergic and anti-inflammatory properties and its use in hydrotherapy.