A survey of sheep with chronic respiratory tract disease was conducted in the central sierra of Peru. Histopathologic examinations coupled with an agar-gel immunodiffusion test for ovine progressive pneumonia (OPP) revealed that sheep pulmonary adenomatosis and OPP were present in these flocks. Of 80 sheep examined, 22 had lesions of sheep pulmonary adenomatosis, and 4 had metastases to regional lymph nodes. Four sheep had lesions consistent with OPP and 9 had lesions indicating the coexistence of both diseases. The agar-gel immunodiffusion test revealed that at least 26% of the sheep had been exposed to the OPP (or an antigenically similar) virus. A variety of other respiratory tract diseases complicated the evaluations of these sheep, including verminous pneumonia, hydatid disease, lung abscesses, and other nonspecific acute and chronic pneumonias.