Expression of HIV-1 Tat alone in mice leads to development of different neoplasms, including lymphomas (Vogel et al., 1988, 1991; Corallini et al., 1993; Altavilla et al., 1999; Kundu et al., 1999), suggesting that Tat protein participates in oncogenesis in HIV-1-infected patients. The gene discussed is TAT; the disease is lymphoma.