Obtaining a viable estimate of the amount of compound absorbed into the skin is important for reasons related to medicinal therapy or to protect human health during exposure to environmental pollutants and toxic compounds. Experimentally determined permeability coefficients are useful for quantifying the dermal absorption of compounds through the skin, and they have been determined for many compounds in many different exposure scenarios. However, measurements do not exist for many compounds with the potential for dermal absorption. Hence the motivation for developing equations to estimate permeability coefficient values based on readily available input parameters. Several equations for estimating the permeability of skin to aqueous organic compounds in terms of the penetrating chemical's molecular weight (MW) and octanol-water partition coefficient (Kow) were reviewed in Chapter 2 along with the databases upon which these equations were developed. We identified numerous measurements in the most commonly utilized databases that are inconsistent with the database in various ways. For example, some measurements were made at an unsteady state; others were measured from vehicles other than water alone, and still other measurements were from animal and not human skin. Also the different penetration rates of ionized and nonionized penetrants were not usually