OBJECTIVE Colony-stimulating factors (CSFs) are well-known hematopoietic growth factors. Although recent studies revealed that CSFs are involved in many inflammatory conditions, the local production of CSFs and its regulation in the kidney is not well elucidated. Therefore, using cultured human proximal tubular epithelial cells (PTEC), we examined the effect of thrombin on CSFs production, since thrombin has been suggested to play an important role in tubulointerstitial injury. METHODS PTEC were incubated with thrombin (0.5-5.0 U/ml) and the effects on the production of macrophage CSF (M-CSF), granulocyte-macrophage CSF (GM-CSF) and granulocyte CSF (G-CSF) were measured in the cell supernatant by enzyme-linked immunosorbent assay, and the expressions of mRNA were analyzed by quantitative real-time reverse transcription polymerase chain reaction. Using argatroban, a direct thrombin inhibitor, we also examined the specific effect of thrombin. RESULTS Thrombin 5.0 U/ml significantly stimulated the production of M-CSF (p < 0.01) and G-CSF (p < 0.01), and 1.0 and 5.0 U/ml thrombin significantly stimulated GM-CSF (p < 0.02 and p < 0.01) in a dose-dependent manner. Thrombin 5.0 U/ml increased CSFs (M-CSF, p < 0.005; GM-CSF, p < 0.0005; G-CSF, p < 0.005) in a time-dependent manner. Thrombin also significantly enhanced the mRNA expressions of M-CSF (p < 0.01), GM-CSF (p < 0.05) and G-CSF (p < 0.01). These effects of thrombin were significantly reduced by the addition of argatroban (M-CSF, p < 0.01; GM-CSF, p < 0.01; G-CSF, p < 0.05). CONCLUSIONS We demonstrated that thrombin significantly increased the production of CSFs by PTEC. These data suggest that the local production of CSFs in the tubulointerstitium may affect tubulointerstitial lesions in kidney injury.