Post-transplantation lymphoproliferative disorder (PTLD) develops in one to ten per cent of transplant recipients and can be EBV-associated. To improve long-term efficacy after rituximab monotherapy and to avoid the toxicity of CHOP seen in first-line treatment, the investigators initiated an international multicentre phase II trial to test whether the subsequent application of rituximab and four courses of three-weekly CHOP would improve the outcome of patients with PTLD: PTLD-1, sequential treatment (ST).