ATP-binding cassette transporter A1 (ABCA1) is a key mediator of cholesterol efflux to apoA-I in lipid-loaded macrophages, which is the first step of reverse cholesterol transport in vivo and a critical step in preventing atherosclerosis. Enhanced ABCA1 expression may inhibit foam cell formation and consequently reduce atherogenic risk. The purpose of this study was to investigate the effect of S-allylcysteine (SAC), the most abundant organosulfur compound in aged garlic extract, on the expression of ATP-binding cassette transporter A1 in human THP-1 macrophages. The human monocyte THP-1 cells were differentiated to macrophage cells in the presence of phorbol 12-myristate13-acetate (PMA). Macrophage cells were then treated with different concentrations (10, 20 and 40 mM) of SAC for 24 h. Total RNA of treated macrophages was extracted and analyzed with real-time RT-PCR. ABCA1 protein expression was also analyzed with western blotting. Results showed that SAC increased the ABCA1 mRNA (1.82-, 2.07- and 2.23-fold) and protein (1.37-, 1.55- and 2.08-fold) expression in macrophage THP-1 cells compared with control (untreated cells). Results suggested that SAC can increase ABCA1 expression in macrophages and may be beneficial in promoting reverse cholesterol efflux. Copyright © 2012 John Wiley & Sons, Ltd.