FREQUENT MUTATIONS: Associated with the high turnover rate of the HIV, frequent inverse transcriptase errors lead to a wide range of possible mutations. Certain mutations can modify the response to antiretroviral agents. The development of resistant strains is mediated by the selection pressure of antiretroviral agents and occurs at a very variable rate depending on the antiretroviral agent used. TO LOWER THE RISK OF RESISTANCE: Persistent replication, whatever the cause, favors the emergence of resistant mutants. Thus the antiretroviral treatment must be initiated early and with the most powerful protocol possible in order to reduce viral replication as quickly as possible. CONTRIBUTION OF VIROLOGY TESTS: It is not always possible to predict the efficacy of antiviral agents from phenotyping and genotyping results. Their use is currently limited to cases of treatment failure. Their contribution in everyday clinical practice remains to be defined.