All patients had vitreous hemorrhage or traction foveal detachment due to PDR. All patients underwent vitrectomy after IV injection of bevacizumab. Either 1.25 mg/0.05 mL or 0.25 mg/0.01 mL of bevacizumab was injected into the vitreous as a preoperative adjunct. Twenty-four consecutive eyes were treated with IV injection of 1.25 mg of bevacizumab between October 1, 2006, and February 29, 2008, and 14 consecutive eyes were treated with IV injection of 0.25 mg of bevacizumab between March 1, 2008, and September 30, 2009. Vitrectomy was performed 1 to 5 days after the injection. An aqueous humor sample was obtained just before IV injection of bevacizumab and just before vitrectomy. The concentration of free VEGF in the aqueous humor was measured with an enzyme-linked immunosorbent assay for human VEGF (Quankine VEGF enzyme-linked immunosorbent assay kit; R&D Systems, Minneapolis, Minnesota). Results were analyzed using SPSS version 12.1 statistical software (SPSS Inc, Chicago, Illinois).