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In this study, the effects of occlusion, octisalate (OS), and propylene glycol (PG) on the in vitro skin permeability of testosterone (TES) have been investigated. TES (either alone or with OS 5% w/v) was applied as a finite dose to full-thickness neonatal porcine skin mounted in flow-through diffusion cells and the amount of TES appearing in the receptor solution (20% v/v ethanol) was determined over 24 h. The skin was occluded with a microscope glass cover slip and to determine the effect of PG, 400 μl of PG/water mixtures (of varying PG concentration) was applied. In addition, the effect of Solugel™ (a proprietary hydrogel containing PG 25% w/w) and Tegaderm™ (a semipermeable film dressing) on the permeation of TES was assessed. Occlusion had no effect on the permeation of TES, however, OS increased the flux of TES 2.9-fold. The concentration of PG which produced optimal TES flux was 20% v/v, and this concentration resulted in a 1.9-fold increase in TES permeation. By combining OS, PG, and occlusion, TES permeation was increased 8.7-fold, which was a synergistic enhancement. In addition, Solugel™ and Tegaderm™, when applied to the skin, produced a similar enhancement in TES permeation to that produced by PG 25% w/w and occlusion.