A prospective pilot study was conducted in patients receiving protease inhibitor-based HAART with a resistance genotype predicting less than two active drugs according to the 2002 ANRS algorithm, CD4 counts over or equal to 100/mm3 and plasma HIV RNA below or equal to 5 log/ml. The treatment was low-dose IDV/RTV (200/100 BID) and 3TC 150mg BID. IDV doses were adjusted at week 4 to ensure a Cmin of 250+/-100ng/ml, which, based on a panel of multi-PI resistant viruses, was calculated to yield an inhibitory quotient (Cmin/IC50) of 0.50. Primary end-points were over 25% decrease in CD4 counts (immunological failure–IF), or over 0.7 log increase in plasma HIV RNA (virological failure–VF) at two consecutive monthly visits during the 24-week study. Inclusions were to stop when the total number of failures (VF+IF) reached 7