Human immunodeficiency virus type 1 DNA synthesis was followed in a CD4+ line of T cells (C8166) grown in the presence or absence of a monoclonal antibody to CD4 that blocks infection By 48 h after infection, cultures grown in the presence of the antibody contained approximately 4 copies of human immunodeficiency virus type 1 DNA per cell, whereas those grown in the absence of the antibody contained approximately 80 copies of viral DNA per cell. Most of the viral DNA in cultures grown in the absence of the antibody was present in a broad smear of apparently incomplete viral sequences. In cultures grown in the presence or absence of the antibody, the 9.6-kilobase linear duplex of viral DNA appeared to undergo integration within 24 h of its appearance. These results demonstrate that T cells accumulate unintegrated human immunodeficiency virus type 1 DNA as a result of multiple virions entering cells.