A two-year longitudinal, microbiological and pathological survey of respiratory disease in lambs housed for fattening at three-and-a-half to four months of age was undertaken. In the first year samples of nasal mucus and blood were taken from lambs each week for the first nine weeks after entry to a fattening unit and each week one lamb was examined post mortem. In the second year two additional fattening units were included in the survey, when samples of blood and nasal mucus were taken from lambs twice weekly for three weeks after entry and two lambs from each unit were examined post mortem eight to 11 days after entry to the unit. In both years the lambs had a nasal discharge and were coughing. Mycoplasma ovipneumoniae and Pasteurella haemolytica were the organisms most consistently isolated from the lungs, trachea and nasal mucus. Mycoplasma arginini and parainfluenza-3 virus were also isolated. Post mortem examination lesions of atypical, pasteurella-type and parasitic pneumonias were seen. In the second year an abattoir survey of pneumonia lesions was undertaken. Areas of pulmonary consolidation were seen in 27.5 per cent, bands of consolidation in 47.5 per cent and muellerius-type lesions in 28 per cent of the lungs examined. No significant correlation was found between the slaughter weights of the lambs and the extent of the lung lesions at slaughter.