Serologic and morphologic studies were carried out with ewes and aborted fetuses, respectively, with regard to the Chlamydial infection in the flocks of some farms. The complement-fixation test was employed to examine a total of 656 blood serum samples. It was found that 20.2 per cent of these contained Chlamydial antibodies. Abortions were established with 6 to 8 per cent of the sheep in each flock. Material was sampled from 35 aborted fetuses. Featuring in the gross lesions of the fetal placenta in Chlamydial abortions were the wheat-bran type of whitish coatings on the surface. Characteristic histologic findings were desquamation, necroses, lympho-leukocytic infiltrations, and the partial deposits of calcium salts. Definite diagnostic value with the aborted fetuses were shown to have the lympho-histiocytic proliferations in the liver, adrenal glands, kidneys, lungs as well as the reticuloendothelial hyperplasia with the presence of gigantic cells of Langhans type in the mesenterial lymph nodes.