As high heterogeneity of plasma composition may be responsible for interference with HIV-1 viral load determination by the bDNA assay, the potential interference caused by a number of plasma components was examined. Among the biochemical substances assayed, cholesterol, bilirubin, and triglycerides did not affect viral load quantification. Hemoglobin did not interfere with the assay at concentrations lower than or equal to 14 g/dl. Above this concentration, measurements decreased by up to 0.78 log, but these hemoglobin levels do not usually occur in the clinical setting. None of the antiretroviral drugs assayed (AZT, dDC, d4T, 3TC and Indinavir) interfered with the measurement. HIV bDNA is a robust assay even in those frequent circumstances in which plasma composition differs notably from normal.