The plant alkaloid camptothecin (CPT) has demonstrated the ability to inhibit replication of the equine anemia virus (E1AV) and the human immunodeficiency virus (HIV) in infected cells in culture. Further, CPT prevented the development of lymphoma and erythroleukemia in mice infected with the Moloney murine leukemia virus and the Friend erythroleukemia virus, respectively, as assessed by prevention or reduction of splenomegaly. These results were observed at concentrations that had no apparent toxic effects on the mice. It has been suggested that the antiretroviral activity of CPT is mediated by the host cell's enzyme topoisomerase I. Taken collectively, the findings indicate that CPT analogues may develop into potent drugs against various human and animal diseases caused by diverse retroviruses. Copyright 1996 S. Karger AG, Basel