Hepatitis C virus (HCV) is one of the most common causes of chronic hepatitis. Interferon is presently the only effective treatment for chronic hepatitis C (CH-C), though its effectiveness is limited. Lactoferrin (LF), which is an 80-kDa, iron-binding glycoprotein, has several biological activities including anti-viral activity, and it was recently reported to inhibit HCV infection in cultured human hepatocytes. The present trial was designed to assess the relationship between the dose of bovine LF (bLF) and the effect of bLF on serum alanine aminotransaminase (ALT) and HCV RNA levels in patients with CH-C. Forty-five patients entered at each of the three dose levels (bLF of 1.8, 3.6, and 7.2 g/day) received orally an 8-week course of bLF. There was no significant relation between the dose of bLF and the effect of bLF on serum ALT or HCV RNA levels. Biochemical (a 50% or greater decrease in the serum ALT level) and virological (a 50% or greater decrease in HCV RNA level) responses were observed in two and four patients, respectively, but all responders relapsed during the follow-up period after bLF treatment. The bLF treatment was generally well tolerated, and no patient had any serious adverse event. In conclusion, the excellent tolerance and potential anti-HCV activity of bLF shown in this trial suggest that further trials using a large number of patients are mandatory. We are currently conducting a double-blind randomized controlled trial comparing bLF with placebo to clarify the anti-HCV activity of bLF in patients with CH-C.