GlaxoSmithKline (GSK) contributes to the public-private pox-protein partnership (P5) which is currently assessing the safety, immunogenicity and clinical efficacy of a prime-boost regimen aimed at preventing HIV transmission (http://www.hvtn.org/en.html). The booster component of the candidate vaccine used in this program consists of two gp120 clade C proteins administered with an adjuvant. In order to inform the selection of the adjuvant in future studies, data on long-term persistence of immunity after vaccination with gp120/AS01 would prove useful. The present study was designed to address this question using a cohort of volunteers vaccinated several years ago with a candidate vaccine containing gp120 and AS01.