The depigmenting activity of 4-isopropylcatechol and hydroquinone, and the behaviour of salicylic acid affecting to the activity were studied. To the hydrophilic ointment base, 4-isopropylcatechol and hydroquinone were incorperated respectively in concentrations of l% and 3%, and to these creams, salicylic acid was also added in concentration of 3% and 5% respectively. These creams were applied topically to the epilated skins of the back of black guinea pigs once a day for 3 weeks. Followings were the results: 1) The depigmenting activity was found to be more potent in 4-isopropylcatechol than in hydroquinone. 2) The depigmenting activity of hydroquinone was found to be remarkably accelerated by the addition of salicylic acid. 3) The skins of guinea pigs were found to be mildly irritated by the application of both 4-isopropylcatechol and hydroquinone.