Abacavir has been associated with myocardial infarction in several studies. This may be related to inflammation and endothelial cell activation. We compared changes in inflammation and endothelial activation markers between antiretroviral-naive adults initiating zidovudine, lamivudine, abacavir, and nonnucleoside reverse transcriptase inhibitor (NNRTI) or this regimen without abacavir. Changes in soluble tumor necrosis factor receptors-I, -II (sTNFR-I, -II), high sensitivity C-reactive protein, and soluble vascular cell adhesion molecule-1 (sVCAM-1) from baseline (pre-ART) to a second time point about 24 weeks after initiating antiretroviral therapy (ART) were compared between groups using multivariable linear regression. A total of 37 met eligibility criteria; 12 received abacavir. The median (interquartile range) age was 37 years (27-45). Most were men (32/37), African-American (15/37), or white (15/37). The median nadir CD4(+) and baseline HIV-1 RNA were 230 cells/mm(3) (180-301) and 82,642 copies/ml (34,400-204,703). In all, 15/30 smoked, 7/37 had hypertension, 1/37 had diabetes, and 1/37 had hyperlipidemia. None had coronary or renal disease. Changes in CD4(+) and HIV-1 RNA level and timing of stored samples with regard to ART initiation were not different between groups. In univariable analysis, log transformed percent change in sTNFR-I (p=0.05) and -II (p=0.04) showed significant between-group differences and trended toward significance for sVCAM-1 (p=0.08). These markers decreased less in the abacavir group. After adjustment for confounders, significantly less decrease for sTNFR-II and sVCAM-1 was seen for those receiving the abacavir-containing regimen. When taken with an NNRTI, abacavir induced a smaller decrease in inflammation biomarkers in this cohort, suggesting a possible proinflammatory effect of this nucleoside analogue.