Nitazoxanide, the first thiazolide, was originally developed for the treatment of Cryptosporidium parvum. More recently, antiviral activity of nitazoxanide against hepatitis B virus (HBV) and hepatitis C virus was recognized in in vitro systems. These basic studies led to phase Ⅱ clinical trials that demonstrated the safety and efficacy of nitazoxanide in combination with peginterferon, with or without ribavirin, in the treatment of chronic hepatitis C genotype 4. The sustained virologic response rate was 79% and 80% in two studies, which was higher than the response rate of 50% with the standard of care with peginterferon plus ribavirin. In very preliminary studies of patients with chronic hepatitis B, nitazoxanide suppressed serum HBV DNA and led to loss of hepatitis B e antigen in the majority of patients and hepatitis B surface antigen in approximately a quarter of patients. Randomized controlled studies of naive and nonresponder patients with chronic hepatitis C genotype 1 are underway, new second generation and controlled release thiazolides are being developed, and future studies of patients with chronic hepatitis B are planned.