An orally administered, killed whole cell pertussis vaccine was developed which proved to be safe and potent in animal experiments. This vaccine was studied in limited field trials in Austria. In these field trials 1 X 10(12) bacterial cells were given orally on days 2, 3, 4, and 5 after birth with an oral booster of 1 X 10(12) cells given at six weeks. This vaccine was tolerated without side effects in more than 20,000 newborns, did induce a specific immune response including anti-pertussis IgG in serum, anti-pertussis IgA in saliva and specific pertussis mitogen stimulation. This immune response occurred significantly earlier in the orally but not in the parenterally vaccinated group. In addition, anti-pertussis antibodies in saliva were not induced in the parenterally vaccinated group. Pertussis morbidity in 11,192 orally vaccinated infants was compared to 3496 infants who did not receive oral vaccination and was found to be significantly lower for up to one year. There was no overall difference between orally and non-orally vaccinated infants as far as pertussis hospitalization and verified pertussis infection after one year was concerned.