The present invention is directed to the transdermal administration of melatonin together with a suitable permeation enhancer. The invention includes a transdermal drug delivery device (10) comprising a matrix (12) adapted to be placed in melatonin- and permeation enhancer-transmitting relation with the skin site (18). The matrix (12) contains sufficient amounts of a permeation enhancer and of melatonin, in combination, to continuously administer to the skin (18) for a predetermined period of time the melatonin to provide an effective therapeutic result. The invention is also directed to a method for the transdermal administration of a therapeutically effective amount of melatonin together with a skin permeation-enhancing amount of a suitable permeation enhancer. The invention further includes methods for time- and rate-patterned transdermal delivery of melatonin to simulate the natural circadian rhythmic profile of melatonin in mammals.