The percutaneous absorption of glycolic acid (g.a.) should be sensitive to pH changes in cosmetic formulations due to ionization. Its in vitro percutaneous absorption through viable human skin was therefore determined from two oil-in-water emulsion formulations, with each adjusted to pH 3.0 and 7.0. Each formulation contained 5% 14C-labeled g.a. After 24 hours, the radioactivity in the receptor fluid, stratum corneum, epidermis and dermis was determined. Total skin absorption of g.a. from formulation A was 27.2% at pH 3 and only 3.5% at pH 7. Formulation B contained an ionic surfactant and resulted in higher absorption (34.8%) at pH 3 but still low absorption (2.3%) at pH 7. Variability in the absorption of g.a. through "normal" human skin was observed and correlated with initial 3H-water permeation values. Formulations A and B were comparable to commercial g.a. products in causing increased 3H-water permeation of hairless guinea pig skin following 24 hour exposures.