To the Editor: I have previously reported a type II diabetic patient complicated with chronic hepatitis C virus (HCV) infection.^[1] Recently, Riva et al^[2] reported an association of truncated CXCL10 with failure to achieve spontaneous clearance of acute HCV infection. They showed that the increased plasma activity of dipeptidyl peptidase-4 (DPP-4) was correlated with the establishment of chronic HCV infection via the generation of a truncated form of the chemokine CXCL10. The study by Riva et al^[2] reminded me of my previous case report. I reported a 56-year-old female patient with type II diabetes complicated with chronic HCV infection, who was successfully treated with the DPP-4 inhibitor, sitagliptin. I retrospectively studied the change in HCV-RNA after the use of sitagliptin. Her chronic HCV infection was treated only with ursodeoxycholic acid, but interferon and direct-acting anti-viral agents were not used. She showed 7.3 log IU/mL of HCV-RNA before the use of sitagliptin in March, 2010. Her HCV-RNA decreased significantly to 5.7 log IU/mL at 15 months after the treatment with sitagliptin in June, 2011. This finding suggested that sitagliptin inhibits DPP-4 and this may prevent truncation of CXCL10, inducing a reduction of HCV-RNA. In another study by Riva et al,^[2] truncated CXCL10 was positively and significantly correlated with HCV-RNA and DPP-4 activity; this supports our hypothesis. Although further studies, preferably with larger numbers of subjects, are needed to elucidate the effects of the DPP-4 inhibitors on HCV infection, DPP-4 may represent a new therapeutic target for the treatment of chronic HCV infection. There is a significant difference in cost between sitagliptin and the currently available directly acting anti-viral treatments. For example, according to the National Institute for Health and Care Excellence in the United Kingdom, a one-month course of once daily sitagliptin costs Great Britain Pound (GBP) 33 whilst the cost of one monthly course of once daily sofosbuvir costs GBP 11 661. The use of DPP-4 inhibitors may produce a significant cost reduction for the treatment of HCV infection.