Helicobacter typhlonius, one of the most recently identified members of this rapidly expanding genus of bacteria, was detected by polymerase chain reaction (PCR) in an animal facility and studied for tissue distribution in sentinel mice ( Helicobacter-free, barrier maintained). Immunodeficient athymic nude- nu ( nu/nu), Helicobacter-sensitive C3H/HeJ and Helicobacter-resistant C57BL/6J mouse strains were used to study whether Helicobacter species could spread to the sex organs and be transmitted vertically. Sentinel mice of these three strains became infected at different times after first exposure and Helicobacter was detected by PCR for a brief period in the sex organs. The potential for PCR-positive tissues from the ovary, uterus, testis and epididymis to transmit infection was investigated via in vitro fertilization (IVF), embryo transfer (ET) or ovary transplantation in immunodeficient athymic nude- nu mice and did not result in contamination of the recipient females.