The authors have studied the relationship among HIV replicative activity, expressed by HIV isolation from peripheral blood lymphocytes and p24 antigenemia detection, and the evolution of infection, in terms of stage of disease and T4 cells absolute number, in a group of 120 infected subjects. Data presented indicate that the expression of viral gene products is related both to clinical and immunological deterioration and suggest that viral replication plays a central role in the progression of the disease.