Animal studies have shown that rectally administrated interferon (IFN) is transferred into the lymphatic system via the rectal mucous membrane, suggesting that an IFN suppository could serve as another drug delivery method. We developed an IFN suppository and administered it to patients with chronic hepatitis C to evaluate its efficacy and safety. Twenty-eight patients with chronic hepatitis C participated in the study. The low-dose IFN suppository containing 1,000 international units (IU) of lymphoblastoid IFNα was administered to 14 patients daily for 24 weeks. Others had a placebo dosing. In 13 of the 14 IFN suppository-treated patients, viral load decreased at week 4. The serum hepatitis C virus (HCV) RNA levels (Log IU/mL, mean±standard error) were 5.65±0.18 before the treatment and 5.17±0.27 at week 4 (P=0.01). The 2'-5' oligoadenylate synthetase activity increased, while the CD4/CD8 ratio decreased significantly. Interestingly, platelet counts and serum albumin levels were significantly increased during and after the treatment. No serious adverse events were observed. The low-dose IFN suppository treatment suppressed HCV replication, modifying host immunity, with increased platelet counts and serum albumin levels. The IFN suppository could be considered a new drug delivery method to preserve the quality of life of patients.