Purpose To investigate the comparative penetration of 0.3% levofloxacin eye drops into the aqueous humour between cataract patients with or without (control) thin-wall filtering blebs. Methods One drop of 0.3% levofloxacin was administered to the eyes at 30-min intervals for 3.5 h before phacoemulcification for both groups. Aqueous humour samples (0.1-0.2 ml) were aspirated during surgery. The concentration of levofloxacin in the aqueous humour was determined by high-performance liquid chromatography. The Student's t-test, Pearson correlation, and v 2 test were used to compare the data of the two groups. A P < 0.05 was required for results to be considered statistically significant. Results The levofloxacin concentration in the aqueous humour was significantly increased (P < 0.0001) in the bleb (mean+SD: 3.7 +/- 2.3 mu g/ml) vs control group (0.4 +/- 0.2 mu g/ml). Intraocular pressure and the bleb area were not correlated with levofloxacin concentration. Conclusion The presence of thin-wall filtering blebs increases intraocular penetration of topically administered levofloxacin.