['To determine if the expression of CD38 on CD8+ T-cells could be used as a marker of viral replication <50 copies/ml in peripheral blood.', 'In a cross-sectional study of patients attending a single HIV clinic in London, an ultra-sensitive HIV RNA viral load assay, with a limit of detection of 3 copies/ml, was used to determine HIV-1 replication in plasma in 70 patients who had sustained viral suppression <50 copies/ml by bDNA assays. Immune activation using the expression of CD38 on CD8+ T-cells was also assessed in patients on antiretroviral therapy (ART) with sustained viral suppression, individuals with persistent low-level viraemia <400 copies/ml and subjects failing ART (viral load >400 copies/mi).', 'There was no significant difference in the percentage of CD8+CD38++ T-cells between patients with <50 copies or <3 copies/ml. Immune activation was significantly increased in patients with persistent low-level viraemia and in subjects failing ART. CD4+ T-cell counts in patients on long-term successful ART are inversely associated with CD8+ T-cell activation.'] Is hIV-1 viral replication below 50 copies/ml in patients on antiretroviral therapy associated with CD8+ T-cell activation?