To determine whether postoperative subconjunctival bevacizumab significantly alters bleb vascularity.A randomized, prospective interventional study.Forty-three eyes from 39 patients were recruited, with 21 eyes randomized to subconjunctival injections of 5-fluorouracil, and 22 eyes to combined 5-fluorouracil/bevacizumab.All patients who underwent uncomplicated primary antimetabolite augmented trabeculectomy who subsequently required postoperative subconjunctival 5-fluorouracil injection within 4 weeks of surgery were eligible. Patients were randomized to receive subconjunctival 5-fluorouracil only (7.5 mg/0.15 mL) or 5-fluorouracil plus bevacizumab (1.25 mg/0.05 mL).Primary outcome was bleb vascularity with secondary endpoints including visual acuity, intraocular pressure, bleb morphology, complications and total numbers of 5-fluorouracil injections were recorded at baseline, week 12 and 18 months.At week 12, there was no significant difference between groups for visual acuity, intraocular pressure, bleb vascularity and morphology, or total number of 5-fluorouracil injections. By 18 months, 47.4% of the 5-fluorouracil/bevacizumab group exhibited central bleb avascularity compared with 21.1% of the 5-fluorouracil group (Fisher's exact test, P = 0.17). Two bleb complications (one blebitis; one suture abscess) recorded in the 5-fluorouracil/bevacizumab group.After a single combined injection, a trend for increased central bleb avascularity was observed, although this effect was not sufficient to reach statistical significance. This, in addition to the occurrence of two bleb-related complications in the bevacizumab group, suggests the need for a larger clinical trial to further evaluate the safety and efficacy of bevacizumab as a modulating agent in glaucoma filtration surgery.