Studied were the occurrence and the etiologic structure of subclinical mastitis of ewes with which mechanical milking was practiced. It was found that as many as 21,9 per cent of the animals responded positively after the Bernburg test. Eight per cent out of the 875 ewes studied were affected with subclinical mastitis. Etiologically, Staphylococcus aureus and Staph. epidermidis were found to take part in the incidence of the disease. Predisposing factors contributing to the outbreak of this type of mastitis were the traumatic injuries of the udder due to the so-called blind milking and the individual deviations in the morphology of the mammary gland. Secretory troubles were found in 11.7 per cent of the sheep.