One challenge in designing clinical trials for treatment of acute GVHD (aGVHD) is the lack of an established standardized end point to measure the success of therapies. To facilitate assessment of end points in clinical trials for treatment of aGVHD in the current allo-SCT era, a national workshop was recently organized. In this study, which was presented at the workshop, we evaluated the prognostic value of response to upfront therapy in a cohort of 83 patients who had been enrolled on two clinical trials testing novel therapies for aGVHD at our institution. Our results indicate that patients whose aGVHD has a CR or PR by day 28 after initiation of systemic therapy have a significantly lower 6-month cumulative incidence of non-relapse mortality (NRM) (16%) than patients whose aGVHD did not respond to therapy by day 28 (48%, P=0.005). Multivariate analysis based on the Cox proportional hazards regression analysis showed that the impact of response on NRM is independent of patient and aGVHD characteristics. Our data confirm the validity of using day-28 response as a primary end point in clinical trials for upfront therapy for aGVHD.