Rats and mice were vaccinated with Haemophilus influenzae in different vaccination schedules whereafter blood eosinophils were counted. In rats a single vaccination resulted in a dose-dependent effect on the blood eosinophil count in a pattern comparable with that after Bordetella pertussis vaccination. In a long-term vaccination schedule (five times a week for 5 weeks) rats developed a constant eosinophilia. In mice a single vaccination resulted in an eosinopenia of a consistent pattern which differed from the response after Bordetella pertussis vaccination; in a long-term vaccination schedule, eosinophilia was evoked for a period of about 13 days. 2. Thirty minutes after an adrenaline injection in vaccinated rats and mice with Haemophilus influenzae, hyperglycaemic and eosinophilic responses were measured. The eosinophilic response after adrenaline was inhibited in both species; the hyperglycaemic response in rats was unaltered, in mice the response was slightly but significantly (P less than 0.05) decreased. 3. The sensitivity to several drugs was tested in mice, 5 days after vaccination with Haemophilus influenzae or Bordetella pertussis. Haemophilus influenzae vaccination reduced the isoprenaline sensitivity and increased the noradrenaline sensitivity. Bordetella pertussis vaccination reduced the isoprenaline sensitivity while the sensitivity to histamine and adrenaline was raised. 4. The Haemophilus influenzae vaccinated experimental animal provides a model that is possibly more related to human atopy than the Bordetella pertussis vaccinated animal.
