A simple method was devised for the establishment of continuous lymphoblastoid cell lines (LCL). Unfractionated mononuclear cells collected from healthy donors were infected in vitro by Epstein-Barr Virus (EBV) (strain B95-8) under specific conditions: an immunosuppressive drug, Cyclosporin-A (CS-A, Sandoz), associated with the use of a feeder layer (MRC-5) led to 100% efficiency of LCL establishment. A bank of 400 LCL was set up for completion of genetic studies. Regression and kinetics of virus-induced transformation were monitored and related to donors' EBV immune status. Mean time of LCL establishment and probability of regression among seropositive donors were not linked to any given value titer of antibodies against Viral Capsid Antigen (VCA) or against Epstein-Barr Nuclear Antigen (EBNA). However, when the anti-VCA:anti-EBNA ratio was considered, this parameter seemed to be linked to the kinetics of transformation but not to the probability of regression. Once LCL are established, large quantities of human cells can be produced. The complete cellular DNA is available so that any part of it can be scrutinized. Moreover, some of the phenotypic characteristics of these B cells can be used for a wide range of investigations.