HIV antigenaemia can be detected at or possibly before the onset of clinical symptoms of primary HIV infection. Approximately one week after the onset of HIV antigenaemia, a primary anti-HIV IgM response may occur. A week later, generally within 3 to 6 weeks after infection, anti-HIV IgG can be detected. After primary infection, most persons enter an asymptomatic stage, often with generalized lymphadenopathy of varying duration. Disease progression is associated with the appearance of persistent HIV antigenaemia and with a decline of antibody reactivity to the viral core proteins p17 and p24.