Hepatitis F is a hypothetical virus linked to hepatitis. Several hepatitis F candidates emerged in the 1990s; none of these reports have been substantiated.
In 1994, Deka et al. reported that novel viral particles had been discovered in the stool of post-transfusion, non-hepatitis A, non-hepatitis B, non-hepatitis C, non-hepatitis E patients. Injection of these particles into the bloodstream of Indian rhesus monkeys caused hepatitis, and the virus was named hepatitis F or Toga virus. Further investigations failed to confirm the existence of the virus, and it was delisted as a cause for infectious hepatitis.
A subsequently-discovered virus thought to cause hepatitis was named Hepatitis G virus, though its role in hepatitis has not been confirmed and it is now considered synonymous with GB virus C and is an "orphan virus" with no causal links to any human disease.