The term "fog fever" was originally used identify a disease of adult cattle grazing lush pastures in the autumn. Unfortunately, the name has subsequently been applied to other respiratory disorders which occurred under different epidemiological circumstances, so that the name "fog fever" has lost much of its original specificity and become almost synonymous with "acute respiratory distress". The pulmonary lesions in 151 cattle, of all ages, with acute respiratory distress are described in this report. While most of the animals were referred as examples of "fog fever", in only 43 of the 151 cases were the clinical signs, epidemiology and post mortem findings consistent with that disease. Twelve other pulmonary disturbances were encountered in the other animals and the pathology of these conditions has bee described.