In vitro mouse skin permeation studies were carried out under imposed temperature gradients across the diffusion cell. The permeation rates were obtained from appearance kinetics, using a newly designed, closed, water-jacketed and internally magnetically stirred diffusion cell. The cell was set up with two baths so that the temperature could be programmed to variable patterns to simulate possible environmental conditions in an attempt to approximate the conditions of absorption of waterborne pollutants out of a reservoir at a non-physiologic temperature and into another 37 C reservoir representing the human body. Permeation rates decreased with decreased temperature but were far higher in non-isothermal studies than rates measured under isothermal conditions at the lower temperatures. Since the stratum corneum acts as the principal barrier to permeation and is in contact with the donor medium, the donor side temperature should have the greatest effect on rates, which it did in these studies. However, measured decreases in permeation when the donor temperature was less than 37 C indicate that either the surface temperature of the skin is appreciably higher than the bulk donor temperature or diffusion in lower strata has measurable impact on rates, or both.