It is a prospective, open, multicenter trial with repeated early TDM (weeks 2, 8 or 16, 24) after the initiation of HAART including either indinavir/r (IDV), lopinavir/r (LPV) or the new 625 mg formulation of nelfinavir (NFV) bid. It was planned to include 99 PI-naïve HIV-1 infected patients over 18 years old, 33 for each PI. Concentrations were measured by HPLC in each center. If trough concentrations were out of the range of 150-500, 2500-7000 or 1500-5500 ng/ml for IDV, LPV and NFV respectively, the PI doses were adjusted possibly more than once during the first 24 weeks of follow-up. Adjustments were done by steps of one pill (200, 133/33 or 250 mg for IDV, LPV/r or NFV, respectively) bid. Failure of the strategy was defined by either two consecutive viral loads over 200 copies/ml between weeks 16 and 48, or a validated PI-related adverse event grade III or IV or a grade II diarrhoea or renal lithiasis. Patients without adverse events before week 16 were defined as assessable if they had at least the virological assessment of week 16.