Samples of colostrum were taken from 180 suckling cows (beef cows) from the same herd, during the 3 hours immediately after calving over a period of 4 consecutive years. Total proteins in colostrum-whey were estimated by the biuret method, and concentrations of gamma-globulins determined by electrophoresis. The significance of the close relationship between calf mortality and gamma-globulin levels in the maternal colostrum was studied. An attempt was made to define levels suitable for the health of the calves. Twin birth, age at calving and food intake towards the end of the gestation period, whatever their effect on calf mortality rate, did not bring about any significant variation in the levels of colostral gamma-globulins. On the other hand, however, cows suffering from various infections had lower levels of colostral gamma-globulins, and produced a higher calf mortality rate. A high degree of repeatability in gamma-globulin levels was observed in colostrums produced by the same cow during successive calvings. A correlation between colostral gamma-globulin levels of a particular cow and those of her female offspring was also found. This result, which should be controlled on a larger number of animals, suggests the possibility of an approach of the problem of calf mortality, using a sanitary and genetic selection designed to reduce the number of cows producing colostrum with low levels of gamma-globulins.