The effects of four essential oils (rosemary, ylang, lilacin, and peppermint oils), and three plant oils (jojoba oil, corn germ oil, and olive oil) on the permeation of aminophylline were studied using human skin. The permeation effects of these oils were compared with those of three chemical penetration enhancers. Although all oils enhanced the permeation of aminophylline, their effects were less than that of ethanol. Jojoba oil was found to be the most active, causing about a 32% peak height decrease of N-H bending absorbances in comparison with the control, while peppermint, lilacin, rosemary, and ylang oils caused 28%, 24%, 18%, and 12% peak height decreases, respectively. Microemulsions containing 10% jojoba oil and 30% corn germ oil were found to be superior vehicles for the percutaneous absorption of aminophylline. Comparision with results obtained from high-performance liquid chromatography shows good agreement.