In this study, diverse in vitro studies were undertaken in order to examine the influence of hair follicles and intrinsic skin structure heterogeneities on transdermal drug delivery. The skin sandwich system was used to investigate the influence of drug partition coefficient on follicular delivery in each of human and porcine skin. To this end, eight different drugs (estradiol, corticosterone, hydrocortisone, aldosterone. cinictidinc, dcoxyadcnosine, adenosine and sucrose) exhibiting a wide range of log ocianol-water partition coefficients but comparable molecular weights were selected. In both skin species, a plot of percentage follicular contribution as a function of solute log octanol-watcr partition coefficient yielded a parabolic relationship.