The authors have studied the penetration of Ofloxacin in the aqueous humour in 30 patients (30 eyes). Six hours after a single oral dose of 200 mg, the concentration in the anterior chamber reached 0.6 microgram/ml which is 23% of the average serum level. It is over the minimal inhibitory concentration necessary for many bacterial agents found in endophthalmitis (except Streptococcus) because the MIC of Ofloxacin are the lowest among quinolones. Side effects and association with other antibiotics are precise.