The effect of various vehicles on the permeation of a model drug, ketoprofen in solution formulation was evaluated using a flow-through diffusion cell system at $37^{circ}C$. To investigate the mechanism of permeation rate enhancement, the effects of pretreatment with various vehicles on the permeation of the drug were evaluated using 5 mg/ml solution and saturated solution. The order of permeation rate of ketoprofen across hairless mouse skin after pretreatment with various vehicles was similar to the case where the vehicles and the drug were coadministered except ethanol and oleic acid. The results indicate that the mechanism of enhancement can be direct action of the vehicles on the barrier property of the skin and/or carrier mechanism.