PURPOSE: Janus kinase (JAK) and spleen tyrosine kinase (SYK) play critical functions in T-cell activation and in inflammation. Because of their antiinflammatory effects, JAK and SYK inhibitors have recently been evaluated in several immunopathogenic disorders. This pilot study was designed to assess the safety and efficacy of a topical combined JAK/SYK inhibitor, R348, ophthalmic solution for treatment of ocular surface disease in graft-versus-host disease (GVHD). METHODS: This phase 2, double-masked, randomized, pilot trial included 30 patients with ocular surface disease due to GVHD who were randomized to receive topical 0.5% R348, 0.2% R348, or vehicle, twice daily for 12 weeks. Before and after treatment, a comprehensive ophthalmic evaluation was performed, which included Ocular Surface Disease Index (OSDI) questionnaire, Ocular Comfort Index questionnaire, corneal fluorescein staining, conjunctival lissamine green staining, and Schirmer test with anesthesia. Changes in these parameters were compared between the 3 groups. RESULTS: The mean decrease in total corneal fluorescein staining at 12 weeks after treatment was higher in the 0.5% R348 group (-6.0 ± 3.9, NEI scoring) compared with the vehicle (-2.1 ± 2.6, P = 0.045) or the 0.2% R348 group (-4.1 ± 3.6, P = 0.34). However, there were no significant differences among the groups in terms of treatment-induced changes in OSDI, Ocular Comfort Index, conjunctival lissamine green staining, or Schirmer scores. R348 eye drops were well tolerated. CONCLUSIONS: This pilot study indicates that 0.5% R348 JAK/SYK inhibitor ophthalmic solution is well tolerated and may have some therapeutic efficacy in treating ocular GVHD. Larger trials are required to derive more definitive data.