Abstract
Three field strains of Mycoplasma dispar were inoculated, by aerosol inhalation, into a total of eight naturally-born, colostrum-deprived calves. All three strains produced macroscopic pneumonia, each in one calf. Histopaithologically an exudative bronchitis accompanied by moderate interstitial cell proliferations was found. Reisolation studies indicated that the entire respiratory tract is the natural habitat of Mycoplasma dispar, which apparently does not spread via the blood stream.