Epstein-Barr virus (EBV)-associated B-cell lymphoproliferative disorders occur at an increasing frequency in various hereditary and acquired states of immune dysfunction. In a few cases of T-cell lymphoma, especially in angioimmunoblastic T-cell lymphoma (AILT), EBV-associated B-cell lymphoproliferative disorders have been reported. Here, we present two cases of EBV-associated B-cell lymphoma after treatment of T-cell lymphoma (AILT and peripheral T-cell lymphoma, unspecified, PTCL-NOS) with a regimen containing alemtuzumab and fludarabine. Conventional and immunohistological tissue staining showed the typical features of highly proliferating diffuse large B-cell lymphoma in both cases. The monoclonal B-cell population displayed EBV latency type III. At the time of diagnosis the cellular immune status of both patients was severely compromised with an absolute CD4 T-cell count below <120 microl(-1). Our observation supports the notion that combination of cytotoxic drugs and immunosuppressive antibodies in patients with T-cell lymphoma may severely aggravate the already present immunodeficiency. We suggest to monitor the cellular immune status in combination with the EBV load in high risk patients for early detection-and possibly intervention-of EBV-associated lymphoma.