Bilayer skin/two-compartment body model was utilized to correlate in vitro skin permeation facts and numbers and in vivo plasma grade facts and numbers after transdermal delivery of verapamil. The good association was discovered between the transient-state profiles of the untested and simulated data. However, the untested steady-state concentrations were smaller than the forecast values. This could be clarified on the cornerstone that verapamil was undergoing bioconversion in human skin. The mathematical form utilized furthermore presents an approximate of the rate unchanging for the metabolism of verapamil in the skin.