Controversy exists as to whether treatment of HIV-1-seropositive hemophiliacs with blood coagulation products of high purity might help prevent the decline of CD4-positive lymphocytes and thus delay progression toward AIDS. As viral load has recently been shown to be associated with disease progression in HIV-1 infection, we tested for a possible direct interference of high- or intermediate-purity blood coagulation products with replication of HIV-1. The data obtained revealed comparable replication of HIV-1 in the presence and absence of all blood coagulation products tested (assessed by PCR-based quantitation of proviral HIV-1 DNA in infected cells after a 10-day incubation period). These data suggest that coagulation factor concentrates per se will also have no direct effect on HIV-1 replication in vivo.