Numerous strategies have been proposed to evaluate melanosome transfer. Methods allowing quantitative measurements of this transfer in human normal cellular models, however, are very few and often require extremely specialized devices that are expensive and difficult to use. As a part of the melanosome-specific membrane-bound glycoprotein, Pmel 17 is released from the melanosome membrane by ectodomain shedding. We reasoned, therefore, that it should be possible to evaluate melanosome transfer by quantifying this "soluble" Pmel 17. The Pmel 17 ELISA assay developed permits a detection of 10 to 1000 ng/ml of this glycoprotein in human normal melanocyte-keratinocyte co-culture media. As expected, niacinamide, a well-known melanosome transfer inhibitor, significantly reduced the Pmel 17 quantities found in the culture media. This validated our experimental design. We then used our model to show that a whitening cosmetic active compound, i.e., an Alaria esculenta extract, can (at least in part) enable a significant decrease in the melanosome transfer to produce a lightening effect without affecting melanin production. This research provides a simple and efficient method to quantify melanosome transfer in a human normal co-culture model. It is a particularly useful tool with which to facilitate the development of new active whitening compounds.