The quantitative assessment of the penetration of organic solvents through skin is necessary for the evaluation of health hazards in occupational environments. We investigated the rate of dermal penetration when mixed or single forms of organic solvents were placed into a diffusion cell in vitro or into an experimental animal in vivo. The diffusion rates of methanol. toluene, and styrene were 6.07, 0.129, and 0.046 mg/$cm^2$/h, respectively. When skin was exposed to the mixed solvent of methanol and toluene, the penetration rate of toluene did not change significantly (0.110 mg/$cm^2$/h). However, the rate of methanol penetration increased to 43.90 mg/$ extrm{cm}^2$/h. The penetration rate of methanol also increased significantly to 54.69 mg/$cm^2$/h by mixing it with styrene. The concentration of methanol in the blood was monitored during the epicutaneous exposure in rats. The blood concentration of methanol was increased by mixing methanol with toluene as seen in the in vitro experiments. These results showed that the penetration rate of organic solvents would be enhanced by mixing them with other solvents.