Nucleic Acid Sequence Based Amplification (NASBA) is a suitable method for the quantification of HIV-1 RNA in plasma and serum samples. Since determination of the viral load appears to be a valuable marker for the prediction of disease progression and for monitoring the efficiency of antiretroviral therapy, the National AIDS Committee initiated the introduction of NASBA in Hungary at the end of 1996. We obtained plasma samples from patients with ARC and AIDS of the Szt. László Hospital, Budapest. We found an increased viral burden in untreated AIDS (CDC group C) patients compared to untreated ARC (CDC group B) patients. In plasma samples of clinically stable ARC and AIDS patients treated with antiretroviral drugs we detected relatively low HIV-1 RNA copy levels while similarly treated ARC and AIDS patients with progressive disease had high HIV-1 RNA copy numbers. The CD4+ T-cell count was lower in AIDS patients compared to ARC patients, as expected. In general, there was an inverse correlation (r = -0.487, P < 0.0001) between CD4+ T-cell counts and HIV-1 RNA levels. We concluded that measurement of HIV-1 RNA plasma level has an important role in assessing prognosis and effects of antiretroviral therapy in HIV-infected patients.