PURPOSE: To assess ex vivo human scleral permeability to triamcinolone acetonide (TA). METHODS: The experiments were carried out using scleral samples and a Franz-type vertical diffusion cell. A suspension containing TA was prepared and placed in the donor chamber. The concentration of TA in the receptor chamber was measured by high-performance liquid chromatography (HPLC) assay and expressed as a percentage relative to TA concentration dissolved in the donor chamber. Control experiments using a commercial TA suspension were performed. RESULTS: TA (+/-SEM) dissolved in the donor suspension was 10.69 +/- 1.28 microg/ml. The diffusion rate of TA varied from 30% after 1 day to 72% after 4 days, after which equilibrium was reached. The human scleral permeability coefficient (P(s) +/- SEM) was 1.47+/- 0.17 x 10(- 5) cm/s. CONCLUSIONS: TA crossed human sclera. The mean amount of drug retained in the sclera increased with time, 4 days being necessary to equilibrate the unidirectional flux. The TA permeability coefficient was comparable to that of other corticosteroids.