Recently, chicken egg yolk was recognized as an inexpensive antibody source, and the therapeutic usefulness of egg yolk immunoglobulin Y (IgY) in oral passive immunization has been investigated. Although multiple antibiotic treatments eradicate most Helicobacter pylori (H. pylori) infections, therapy fails in 10-15% of cases due to the development of drug resistance. Consequently, it is important that new, more broadly based therapies for the treatment of H. pylori infection should be identified. The present study evaluated the effect, on H. pylori infection, of IgY prepared from egg yolk of hens immunized with H. pylori urease (anti-HpU IgY). Seventeen asymptomatic volunteers diagnosed as H. pylori-positive by the 13C-urea breath test (UBT) were orally administered anti-HpU IgY for 4 weeks. Four weeks later, UBT values were significantly decreased although no case showed H. pylori eradication. An H. pylori-positive 53-year-old female gastritis patient administered anti-HpU IgY plus lansoprazole for 8 weeks showed a decrease in serum pepsinogen (PG) I and UBT values as well as an increase in the PG I/II ratio. In conclusion, anti-HpU IgY may mitigate H. pylori-associated gastritis and partially attenuate gastric urease activity. Furthermore, anti-HpU IgY combined with antacids appears to ameliorate gastric inflammation. These encouraging results may represent a novel approach to the management of H. pylori-associated gastroduodenal disease.