The infectivity and migratory pattern of Ancylostoma ceylanicum infective larvae (L3) were investigated in hamsters infected by various routes. Following oral administration 40-70% of L3 attained maturity and there was no tissue migration. Following subcutaneous inoculation a small number (1-1.2%) of L3 attained maturity in the intestine after completing the broncho-oesophageal journey. Larvae which penetrated the skin also became adult in the intestine. Most of the larvae entering parenterally remained at the site of infection and in the tracheal region for more than 100 days without undergoing any development, other than desheathment. Those transmitted orally to naive hamsters developed in the normal way. Larvae inoculated parenterally into female hamsters were able to infect offspring in milk, but could not cross the placental barrier.