Quantitative immunoglobulins were measured in canine serum, colostrum, milk and intestinal secretions, and normal mean values were established. Two groups of dogs, pure bred and mongrel, were used because of significantly different serum levels of IgG subclasses IgGa,b and IgGd. The immunoglobulin content of breast secretions diminished during the 1st week post-partum and only IgA persisted in appreciable amounts until weaning. Intestinal fluid was immunoglobulin-poor except for high levels of IgA, which reaffirms the secretory origin of the molecule.