A method for determining whether an individual infected with HIV-1 has an increased likelihood of being hypersusceptible to treatment with a protease inhibitor, comprising detecting, in a sample from said individual, the presence or absence of a mutation associated with hypersusceptibility to treatment with said protease inhibitor at amino acid position 16, 20, 33, 36, 37, 39, 45, 65, 69, 77, 89 or 93 of the amino acid sequence of the protease of the HIV-1, wherein the presence of said mutation indicates that the individual has an increased likelihood of being hypersusceptible to treatment with the protease inhibitor, with the proviso that said mutation is not L33F.