SummaryThe soluble A‐substance has been found in the serum, milk and saliva of all A‐positive sows with the exception of one serum from a sow of Ap phenotype. A‐substance inhibition activity has been measured. High titres were found in the saliva of the Ac group and in Ap phenotypes.In addition to the previously described presence of soluble Na and Nb substances in the serum, both these substances were also found in nearly the same level in the milk of sows of appropriate phenotypes.The saliva of pigs does not contain soluble Na or Nb subst