We have found that an HIV-1 accessory gene product Vpr enhanced HIV-1 reproduction in U1 cells chiefly by the induction of TNF, a proinflammatory cytokine, which was also known to be an activator of HIV-1 reproduction. We have generated the functional HIV-1 accessory gene product Vpr in bacterial cells. Vpr was generated in an Escherichia coli system (rVpr), purified with antibodies (Ab) to the 16 C-terminal amino acids of Vpr. The purified rVpr of 15 kDa was examined for its ability to upregulate HIV-1 reproduction in U1 cells, which is a reported function of the authentic Vpr. rVpr upregulated HIV-1 reproduction in U1 cells in a dose-dependent manner and induced the secretion of TNF. The upregulation of HIV-1 by rVpr was completely inhibited not only by anti-Vpr antibodies but also by anti-TNF antibody. These findings suggested that Vpr caused an HIV-1 reproduction in U1 cells through the induction of TNF.