After a detailed review of the literature availabe on the problems of immunoglobulin level in colostrum and blood serum of calves and after a discussion of its impact on health condition, the following investigations on this subject are presented. 1. Calves to fail ill in the rearing period show significantly lower serum Ig levels even during the first two days of life, when they are still clinically healthy, as well as up to the end of the first week of life than those of calves remaining in good health. 2. Ig values sharply rise during the disease period, IgA and IgM responding more rapidly than IgG. 3. In calves suffering from a disease of the gastrointestinal tract serum IgM titer is lowest, while in calves suffering from a disease of the respiratory duct serum IgA titer is lowest and in those suffering or dying from both disease complexes all Ig titers are reduced. 4. Calves showing high serum Ig levels during the first three days of life reveal higher daily gains in weight than those with lower serum Ig levels during that period.