Objective: This phase 1 trial set out to examine the safety of a bacteriophage-based preparation for difficult-to-treat wounds. Method: The intention-to-treat sample comprised 42 patients with chronic venous leg ulcers (VLUs); 39 patients completed the trial. The ulcers were treated for 12 weeks with either a saline control or bacteriophages targeted against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli. Follow-up continued until week 24. Results: No adverse events were attributed to the study product. No signifi cant difference (p>0.05) was determined between the test and control groups for frequency of adverse events, rate of healing, or frequency of healing. Conclusion: This study found no safety concerns with the bacteriophage treatment. Efficacy of the preparation will need to be evaluated in a phase II efficacy study. Declaration of interest: One of the authors (AS) holds an equity interest in Intralytix. The other authors do not have any interest in commercial activities.