In spite of their clinical relevance, however, conventional resistance tests are insensitive and underestimate antiretroviral resistance. By means of new ultrasensitive resistance tests it is possible to detect resistant viruses in minority populations that remain undetected by conventional genotypic tests. Ultrasensitive resistance tests thus double or triple the number of patients in whom antiretroviral resistance is detected. It is important to emphasize that detection of minority resistant mutants in antiretroviral naïve patients increases more than triples the risk of virological failure. The clinical impact of detecting minority resistant variants in treatment-experienced patients with therapeutic failure remains unknown.