The transfer of immunoglobulins (Ig) by colostrum from the queen to the neonatal kitten not only provides protection from infection, but may also cause serious illness. Neonatal isoerythrolysis may occur when kittens of blood type A or AB receive colostral anti-A alloantibodies from a type B queen. In contrast to other species, Ig concentrations in milk and colostrum did not differ markedly. Gastrointestinal absorption of IgG was limited to the first day of life. The half-lifes of maternally derived IgG and IgA in kittens were shorter than in puppies. In conclusion, milk from another queen may be given as a replacement for colostrum to neonatal kittens. Kittens at risk of neonatal isoerythrolysis must be removed from their type B queen during the first day of life and may safely receive milk or colostrum from a type A queen.