Acquired immunodeficiency syndrome (AIDS) is caused by a retrovirus, the human immunodeficiency virus (HIV), which belongs to the lentivirus subfamily. The research program of the human retrovirology unit is aimed at understanding the function of a specific set of HIV-1 proteins- the so-called accessory proteins Vif , Vpr, Vpu, and Nef – which are not commonly found in other retroviruses. While in most cases the molecular basis of accessory protein function is not fully understood, it appears that these viral proteins share a common mechanistic strategy in that they are generally devoid of enzymatic activity. Instead, they act as multifunctional adapters capable of recruiting and modulating basic host cell processes to regulate wide-ranging aspects of viral replication and pathogenesis including viral infectivity (Vif, Nef and Vpu), viral gene expression (Vpr), progeny viral production (Vpu) and cell killing (Nef, Vpr, Vpu). The overall goal of the research projects pursued in the human retrovirology unit is to understand the functional role of HIV-1 accessory proteins during viral replication and pathogenesis and to elucidate in molecular and cellular terms their mechanism of action. Ultimately, the elucidation of the interaction between HIV-1 accessory proteins and host cells will lead to an improved understanding of viral replication and pathogenesis as well as suggesting additional targets for antiviral strategies, more of which are urgently needed, in both developed and developing countries.