The protease and reverse transcriptase (RT) genes were studied in antiretroviral (ARV)-experienced and drug-naive HIV-1-infected individuals in Libreville, Gabon. We have shown, although on a limited number of samples that in 58% (11/19) of the patients, with a mean of 17.7 months of ARV drug experience, major mutations inevitably inducing resistances to ARV drugs were present. Resistance was mainly observed to the NRTIs (nucleoside analogue RT inhibitors). This high prevalence may reflect inappropriate ARV drug use. In order to avoid the rapid emergence of resistant viruses on a large scale in the developing world, it is important that the infrastructures necessary to monitor ARV treatment are also rapidly implemented in these countries and that clinicans are trained in the appropriate use of ARV drugs. A continuous surveillance of the circulation of ARV drug-resistant viruses must be organized to guide ARV treatment strategies and policies.