Human breast milk contains many enzymes, some of which may assist in digestion; other enzymes may have other diverse functions. The loci and regulation of milk enzyme synthesis remain to be elucidated, but multiple loci and complex hormonal regulation seem to be likely. In a similar fashion, multiple mechanisms of protein release have been described, but stimulus secretion coupling has not been directly demonstrated. The possible physiologic importance of milk as compensatory mechanisms for the relatively limited digestive capabilities of young infants is but one of many reasons why breast milk should not be heated, if possible, prior to feeding.