Rabbit ATG has been used in two randomised trials to reduce acute Graft versus Host (aGVH) disease in recipients receiving progenitor cell transplants.  While higher doses (15 mg/kg) reduced aGVH this was offset by increased infections. However a long term follow up showed that at both high and low ( mg/kg) doses chronic GVH (cGVH) was reduced.  A similar trial of anti-lymphocyte globulin showed a trend in reduction of aGVH that was not statistically significant, but a reduction in cGVH.  The Canadian Blood and Marrow Transplant Group is currently conducting the first randomised trial in cGVH using an even lower dose of rabbit ATG ( mg/kg) in an attempt to confirm these observations. The endpoint is the reduction in the proportion of patients with cGVH at 1 year, off immunosuppressants .