In this preliminary report, dealing with the biological properties of Avène spring water, we investigated its effects on membrane properties of cultured human skin fibroblasts used as a model cell system. It is shown that incubation of these cells in the presence of Avène spring water brings about an increase in the fluidity of plasma membrane. This effect was evidenced by a decrease in the fluorescence anisotropy of the lipophilic probe diphenylhexatriene and by a 3-fold increase in the lateral diffusion coefficient of the lipophilic probe 5-(N-hexade-canoyl)-aminofluorescein, as measured through fluorescence recovery after photobleaching experiments. This effect reached a maximum for incubation times longer than 30 min and for a dilution of Avène water in laboratory water to about 20–25%. As discussed, changes in the hydrodynamic properties of cell membranes induced by Avène water provide a plausible explanation for some of the biological events this spring water is known to trigger.