In subgroups of two phase 3 studies, patients with high-risk features for failure of antiretroviral therapy, such as a low CD4 count, high base-line level of human immunodeficiency virus (HIV) type 1 RNA, or unfavorable genotypic or phenotypic sensitivity score, raltegravir was superior to placebo in terms of a virologic response at 48 weeks. However, among these patients, in whom antiretroviral therapy had been used previously, 23% of raltegravir recipients had virologic failure by 48 weeks. In patients with high-risk features for failure of antiretroviral therapy, raltegravir was superior to placebo in terms of a virologic response at 48 weeks. However, among these patients, in whom antiretroviral therapy had been used previously, 23% of raltegravir recipients had virologic failure by 48 weeks. Despite the substantial decrease in mortality and morbidity rates associated with highly active antiretroviral therapy over the past decade, there is still a substantial need for effective antiretroviral drugs for patients infected with resistant human immunodeficiency virus type 1 (HIV-1). 1 , 2 The majority of licensed antiretroviral drugs belong to three classes targeting either the HIV-1 protease or reverse transcriptase, and considerable cross-resistance exists among drugs within each class. 3 , 4 In patients with resistant virus, use of antiretroviral agents from new classes offers considerable potential benefit because of the absence of cross-resistance. 5 – 7 HIV-1 integrase represents a new therapeutic target. 8 , . . .