['The aim of this study was to evaluate whether or not combination therapy of pegylated interferon (IFN) and ribavirin for chronic hepatitis (CH) C patients enhances the serum level of KL-6, a sensitive marker for interstitial pneumonia.', 'CH C patients proven histologically and treated with combination therapy of pegylated IFN-alpha-2b and ribavirin, IFN monotherapy or untreated for 48 weeks were retrospectively selected in chronological order in groups of 25. Serum levels of KL-6 were measured by enzyme-linked immunosorbent assay by use of serum stored at -80 degrees C before and at 12, 24, 36, 48 weeks after the initiation of treatment or follow up.', 'The average serum KL-6 levels in patients treated with combination therapy of pegylated IFN and ribavirin increased by 21% at 12 weeks after the start, 23% at 24 weeks, and 28% at 48 weeks. In patients treated with combination therapy of pegylated IFN and ribavirin, the serum KL-6 level significantly increased during treatment. Patients achieved an elevated serum KL-6 level of more than 450 U/ml with statistical significance when: 1) combination therapy was given (P=0.011), 2) serum KL-6 level pretreatment was high more than 300 U/ml (P=0.014).'] Is serum KL-6 level elevated in chronic hepatitis C patients with combination therapy of pegylated interferon and ribavirin?