['To study the inhibitory effect of shikonin on the proliferation of human airway smooth muscle cells (HASMCs) in vitro.', 'HASMCs from the trachea were obtained by primary culture of the tissue explants and adherent culture. The HASMCs were exposed to shikonin at 0 (control group), 0.5, 1, 2, 5, 10, 20, and 40 micromol/L for 12, 24, and 48 h, after which the cell proliferation was assessed by 3-(4,5-carboxymethoxypheny1)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) colorimetric assay. Flow cytometry was used for cell cycle analysis of the HASMCs exposed to shikonin at 40, 20, 10, 5 micromol/L and 0 micromol/L (control group) for 24 h. Immunocytochemistry with SP method was performed to detect the expression of proliferating cell nuclear antigen (PCNA) in the HASMCs treated with shikonin at 20 micromol/L and 0 micromol/L (control group) for 24 h.', 'Shikonin at the concentrations of 20 and 40 micromol/L significantly inhibited the proliferation of the cells (P<0.05), and the effect was especially obvious after 48 h of cell exposure, with inhibition rates of 30.1% and 42.9%, respectively. No significant difference was found between the two concentrations for their cell growth inhibition effects (P>0.05). Shikonin at the concentrations of 20 and 40 micromol/L caused significant cell cycle arrest in G(0)/G(1) phase (P<0.05), the effect of which, however, was not concentration-dependent (P>0.05). Shikohin at 20 micromol/L significantly down-regulated the expression of PCNA in the cells (P<0.05).'] Does [ Shikonin inhibit the proliferation of human airway smooth muscle cells ]?