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 phaseⅡclinical 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. 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 vitro strains. 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. very very preliminary studies of patients with chronic hepatitis B, nitazoxanide suppressed serum HBV DNA and led to loss of hepatitis B antigen in the majority of patients and hepatitis B surface antigen in about 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.