The HLA B5701 Strip test allows the determination of the HLA B5701 alleles. Since the introduction of combined antiretroviral therapy, HIV infection has gone from being a serious and fatal disease to one which is chronic but controllable. Antiretroviral therapy usually entails combining 2 nucleosides which are analogous to reverse transcriptase inhibitors and either an HIV protease inhibitor or a non-nucleoside reverse transcriptase inhibitor. These drugs are very effective but they are associated with a series of undesired effects, such as severe hypersensitivity reactions, especially in the case of therapies using abacavir or nevirapine.Abacavir is used in the treatment of HIV-1 infection since 1999. The WHO recommends abacavir as a second-line treatment, owing to the risk of hypersensitivity associated with its use, which affects 5-8 % of Caucasian patients.Several studies have demonstrated the existence of a strong predictive correlation, in Caucasian populations and groups of Hispanic ethnicity, between hypersensitivity to abacavir and the presence of the HLA-B5701 allele. This correlation is strong enough to enable us to predict the risk of hypersensitivity to abacavir and classify individuals as low (70 %) risk, based on the absence or presence of the HLA-B5701 allele.