Investigations on the effect of colostrum feeding in 1--4-day-old newborn infants on serum proteins and their immunoglobulins were carried out. The values for serum total proteins, albumin and gamma globulins are higher in colostrum-fed infants than the artificially fed group. Immunoglobulin G and immunoglobulin A levels were significantly higher, while immunoglobulin M level was only slightly elevated in the former group. On the other hand, serum total proteins as well as albumin and gamma globulins levels were decreased in lactating compared with non-lactating females, while the alpha and beta globulins levels were higher for lactating than controls. For individual immunoglobulins; IgG level was lower and IgA, IgM levels were higher for lactating than non-lactating females.