The aim of this study was to evaluate efficacy of highly active antiretroviral therapy (HAART) in 64 HIV-1 positive treatment-naive and previously treated patients, with different viral load at baseline. The HAART regimen consisted of one protease inhibitor and two reverse-transcriptase inhibitors. Plasma RNA viral load was measured by RT-PCR (Roche Amplicor Monitor kit) at enrolment and at months 3, 6, 9, and 12 of follow-up. The viral load fell below the threshold of 200 copies/ml in 46.9% of patients at month 6 and this result lasted up to month 12 of follow-up in 42.2% of patients. In these patients the CD4+ cell count increased from a baseline with a median of 194 cells/mmc at month 12. Treatment failure occurred in 35.9% of patients and the proportion was higher among previously treated patients. 7 patients stopped therapy because of poor compliance and 5 because of adverse drug effects. Also in our cases the HAART regimen showed more efficacy in treatment-naive patients, whereas baseline viral load >1x105 was the cause of less efficacy of therapy.