HIV RNA was quantified in blood plasma from 209 patients and in control specimen comparing the NucliSens(TM) HIV-1 QT test (Organon Teknika), which is based on the nucleic acid sequence amplification procedure, and the Quantiplex(TM) 3.0 test (Bayer), which uses hybridization signal enhancement by branched DNA (bDNA) probes. A highly significant correlation (P = 0.01) was found between the two methods with 88% of the samples showing similar results. In cases of discrepant findings, higher virus load was observed with either test (14 x NASBA > bDNA; 12 x bNDA > NASBA). Differences could neither be related to clinical features nor to divergent virus subtypes. Standard preparations containing 35 000 and 222 000 copies were quantified with intra-assay coefficients of variation of < 20% using both methods. A preparation of 192 copies was measured with lower precision by bath tests, yet was detected more reliably by the bDNA method. (C) 2000 Published by Elsevier Science B.V.