BACKGROUND: Oxidized low density lipoprotein plays an important role in development of foam cells in atherosclerosis. The study was focused on regulation of primary human monocyte growth and CD11b expression in presence of nigella sativa oil. METHODS: Primary human monocytes were isolated from whole blood and grown at 37?C and 5% CO? saturation for five days prior to treatment with nigella sativa oil. The cells were plated and washed before treatment with ox-LDL (10 ?g/ml) as positive control and combined treatment of ox-LDL (10 ?g/ml) and (140 ng/ml) nigella sativa oil. The growth progression was monitored every 24 hours for 3 days. RESULTS: Macrophages showed reduced growth in comparison to monocytes 24 hours after treatment with nigella sativa oil. The mean cell diameter was significantly different between untreated and treated condition in monocytes and macrophages (p < 0.001). Similarly, intracellular lipid accumulation was hindered in combined treatment with nigella sativa oil. This was further supported by cell surface expression analysis, where CD11b was markedly reduced in cells treated with combination oxLDL and nigella sativa oil compared to oxLDL alone. More cells differentiated into macrophage-like cells when monocytes were supplemented with oxidized LDL alone. CONCLUSIONS: The finding provides preliminary evidence on regulation of cell growth and differentiation in monocyte and monocyte-derived macrophages by nigella sativa oil. Further investigations need to be conducted to explain its mechanism in human monocyte.