One-week-old human M-CSF differentiated monocyte-derived macrophage cultures were incubated 1 day with 50 μg/ml AcLDL to enrich macrophages with cholesterol. Following rinsing, macrophage cultures were incubated 1 day with the indicated additions (20 μg/ml ApoA-I, 100 μg/ml peptide, and 125 μg/ml sphingomyelin alone or complexed with100 μg/ml peptide 5A) without AcLDL. Then, the macrophage total cholesterol content was determined, and the decrease in macrophage total cholesterol content induced by the added agent was calculated. Macrophage total cholesterol contents before and after incubation with AcLDL were 98 ± 2 nmoles cholesterol/mg cell protein (5 ± 3% cholesteryl ester) and 305 ± 7 nmoles cholesterol/mg cell protein (30 ± 1% cholesteryl ester), respectively. The percentage decrease in net total cholesterol accumulation is listed above the bar. ApoA-I, 5A, and 5A-SPH were all significantly different than EE and SPH. AcLDL, acetylated low-density lipoprotein; f/b, followed by; ApoA-I, apolipoprotein A-I; 5A, peptide 5A; EE, peptide EE; 5A-SPH, peptide 5A-sphingomyelin complex; SPH, sphingomyelin.