The sorption of aluminum complexes to guinea pig stratum corneum has been studied using our previously described fluorometric and atomic absorption spectrophotometric procedures. The sorption, desorption, and binding properties of the two aluminum systems most often used in topically applied antiperspirants, aluminum chloride and aluminum chlorohydrate, Al2(OH)5Cl . 2H2O were examined as a function of aluminum concentration, sorption time, state of hydration, and for various delipidized tissue specimens. The results indicate rapid uptake of aluminum species in both systems from aqueous solutions for partially hydrated tissue, reaching 50% saturation levels in about 30 min. Pseudo-equilibrium sorption isotherms follow a Langmuir-type sorption behavior over the 10(-4) M to 5 x 10(-3) M aluminum concentration range for both systems reaching plateau sorption capacities. At higher aluminum concentrations, however, the aluminum chlorohydrate isotherm exhibits a long linear increase in sorption following this initial plateau. Sorption of the various aluminum species depends on the hydration state of the tissue with increases in sorption of 2- to 3-fold over tissue prehydration time periods of 0-96 hr. Desorption studies indicate significant reversibility of aluminum chloride sorption from partially hydrated tissue but little desorption from fully hydrated tissue. In contrast, little desorption is observed with aluminum chlorohydrate regardless of tissue hydration levels. These differences are interpreted in terms of the inherent physical-chemical properties of the species contained in these two aqueous aluminum (III) ion systems.