Transdermal devices are now marketed for the delivery of systemic medication through the skin. Advantages associated with transdermal drug delivery include avoidance of first-pass metabolism and variable absorption as well as improved patient compliance. Drugs currently available by this route include scopolamine, nitroglycerin (glyceryl trinitrate), estradiol, nicotine, clonidine, fentanyl, and testosterone. This novel development has brought about a specific constellation of skin problems which vary widely in incidence between drugs. It is important to vary the site of drug administration to minimize these reactions. Any eczematous reaction can be treated with a moderately potent topical corticosteroid. Patients with topical sensitivity are usually tolerant of oral challenge but systemic sensitization has been reported and caution is still advocated before proceeding to this step. The increasing use of transdermal drug delivery systems across many specialities means that problems of skin sensitivity are of growing relevance to the dermatologist, the hospital specialist, and the primary care physician.