The capacity or copaiba oil to act as a skin penetration enhancer for the depigmenting agent kojic acid was evaluated using an in vitro diffusion system with static flux and shed rattlesnake skin membrane, Crotalus durissus terrificus, in saline solution at 34 +/- 2 degrees C as the fluid receptor. The quantities of kojic acid liberated into the fluid receptor were determined by spectrophotometry at 268 nin with intervals of one and a half hours. The membranes, pretreated with copaiba oil at 25% and 50% v/v, gave flux values of 8.0 and 12.7 mu g/cm(2)/h, permeability values of 2.0 and 3.3 cmx10(-4)/h, and promotion factors of 4.1 and 3.7, respectively. These results indicate that copaiba oil, at the two concentrations studied, has the capacity to promote penetration of kojic acid.462363370