The authors studied the in vivo phagocytic activity of the uterine leucocytes of cows following delivery of dead or weak calves. The phagocytic indices of uterine leucocytes in examined cows were twofold lower on the 8th and 12th days than those on the 1st and 4th day of puerperium. The factors depressing the phagocytic ability of leucocytes of cows delivering dead or weak calves were discussed.