The aim of this work was to develop an in vitro method for testing the water resistance of sun products. For comparison, we used the in vivo method put forward by the Colipa. Standards and commercial products were successive baths. The Sun protection factor of these different creams was determined in vitro both before and after the baths. The result was that two successive baths of 20 min in moderately shaken distilled water, at 29 +/- 2 degrees C and may substitute the in vivo test.