• The penetration of amikacin sulfate into the anterior chamber of the human eye was determined by radioimmunoassay. Bactericidal concentrations of amikacin were not achieved by topical or intravenous administration. Subconjunctival injection did not produce consistent bactericidal concentrations of amikacin in aqueous humor. Poor corneal penetration and subsequent tight binding to iris pigment are responsible for these observations. Tissue or pigment binding is adsorptive, nonspecific, and readily reversible. Amikacin released after being bound retains its bactericidal potency.