The PTLD-1 trial demonstrated the efficacy and safety of sequential immunochemotherapy with 4 courses of rituximab IV followed by 4 cycles of CHOP chemotherapy. Compared to trials of rituximab monotherapy in PTLD, median overall survival was extended from 2.4 to 6.5 years. Compared to previous trials of chemotherapy, complications were reduced. In addition, we noted that those patients who already had a good response to the first four cycles of rituximab did better overall than those who did not. As a consequence, the PTLD-1/3 trial introduced risk-stratification in sequential treatment according to the response to the first 4 courses of rituximab monotherapy. Those patients with a complete remission went on to receive four further courses of rituximab whereas those who did not received rituximab and CHOP chemotherapy. Interim results have demonstrated that it is safe to restrict chemotherapy treatment in this manner and thus established the concept of treatment stratification based on the response to rituximab.