To be approved for marketing, a potential generic pharmaceutical product must demonstrate bioequivalence, that is, a rate and extent of absorption similar to those of the currently marketed ("innovator") product. For oral products, design and statistical analysis for studies conducted to determine whether two products are bioequivalent have become reasonably standardized; the design is crossover, and analysis is based on the two one-sided tests principle. The purpose of this overview is to consider whether the practices for oral products apply to topical products, and where different procedures may be required. The principles behind the practices for oral products are seen, largely, to carry over to topical products.