Aim To investigate whether homocysteine (HCY) induce the expression of secretory macrophage inflammatory protein-1α (MIP-1α)in THP-1 monocytes. Methods After exposure of the cultured THP-1 monocytes to HCY at increasing concentrations (0.05, 0.1 and 0.2 mmol/L) for 8 h, or at a concentration of 0.1 mmol/L for different incubation times (4, 8 and 16 h), enzyme-linked immunosorbent assay (ELISA) was used to determine MIP-1α protein expression in the cultured supernate of each group. Conditioned media with or without HCY (0.01 mmol/L) were collected for chemotaxis assay by micropore filter method using a modified Boyden Chamber. Results ELISA showed that the exposure of THP-1 monocytes to HCY at different concentrations and for different times induced higher production of MIP-1α protein compared with the control (p<0.01). The MIP-1α protein in cultured supernate was increased in a dose- and time-dependent manner. In chemotaxis assay, the migration distance of monocytes in HCY stimulating group was 83.2±4.8 μm, which was significantly longer than that in the non-HCY stimulating group (73.2±2.3 μm) and random migration group (62.4±3.5 μm)(F=310.70, p<0.01). After adding goat anti-human MIP-1α antibody, the monocyte chemotactic activity was noticeably inhibited, compared with the HCY stimulating group without specific antibody (p<0.01). Conclusions HCY can induce THP-1 monocytes to express MIP-1αand secret into culture medium, which share partial chemotactic activity for peripheral monocytes, and may play an important role in atherogenesis through promoting the recruitment of monocytes into arterial intima.