We have examined 3 different EBV-carrying B cell lines, in terms of ability to be super-infected by the human immunodeficiency virus (HIV-1), and have followed these lines, after infection by HIV-1, over a period of 3 months. We found significant variation among different HIV-1 strains in terms of the multiplicity of infection required to initiate infection in these EBV-positive cell lines. Persistent infection by HIV-1 in the absence of detectable cytopathic effects could be demonstrated, as evaluated by a variety of techniques, including reverse transcriptase assay and immunofluorescence. The results indicate also that all of these cell lines produced progeny HIV-1 intermittently, with large amounts of virus production on some days but not others. In contrast, they were all able to continuously express p24.