he most significant advance for clinical practice is the correlation between the presence of the HLA-B*5701 allele and hypersensitivity reaction to abacavir. In particular, one clinical trial with a large number of patients from distinct ethnic groups found that the probability of not developing hypersensitivity reaction (immunologically confirmed) was 100% if the patient was HLA-B*5701-negative. These data suggest the need to implement this test in daily clinical practice.