At the present time, establishing the bioequivalence (BE) of topical drug products is not a simple process: in contrast to oral medications, costly and time-consuming clinical trials are required for most topical products. In the United States there are provisions within the regulations that allow other methods (i.e. surrogates for clinical trials) to be used to establish BE. The stated preference of the Food and Drug Administration (FDA) is for pharmacodynamics effect studies, but in vivo animal studies as well as in vitro studies are potentially acceptable. Although there is currently only one approved surrogate test within the topical products area (the “skin blanching” or “vasoconstrictor assay” for glucocorticoids), FDA activity over the past twenty five years through sponsored scientific meetings and research, as well as in-house research and initiatives, has led to the development of several alternative test methods for topical products.