The aim of this study was to determine the penetration of intravenously administered meropenem into the human aqueous humor and vitreous. Thirty patients about to undergo cataract surgery and fourteen patients about to undergo vitrectomy received a 2 g dose of meropenem before surgery. Specimens of aqueous humor or vitreous and blood were obtained intraoperatively and analyzed by high performance liquid chromatography (HPLC). The study was designed as a non-randomized prospective trial. Thirty min to 12 hr after administration, mean aqueous humor levels of 13.4 and 1.1 mg/l and vitreous levels between 8.94 and 1.08 mg/l were found, respectively. The peak concentrations are distinctly above the in vitro measured minimum inhibitory concentration of meropenem for 90% (MIC90) of almost all relevant gram-positive and gram-negative organisms, including Pseudomonas aeruginosa and Enterobacteriaceae. With regard to its broad spectrum, high antibacterial activity, and good penetration into ocular fluids, meropenem seems to be an alternative to currently used systemic drugs. Its usefulness in perioperative prophylaxis, as initial therapy after perforating or penetrating injuries, or in the therapy of bacterial endophthalmitis has yet to be proved.