With the exception of infant growth, there are no well-defined parameters describing normal human lactation. This represents a major gap in the continuum of care that does not exist for other major organs. Biological normality occurs naturally and is characterized by well-integrated function. We have proposed a definition that highlights four key elements that describe parameters for biological normality: comfort, milk supply, infant health, and maternal health. Notwithstanding the current limitations, published data have been collated to provide preliminary markers for the initiation of lactation and to describe objective tests once lactation is established. Reference limits have been calculated for maternal markers of secretory activation, including progesterone in maternal blood and total protein, lactose, sodium, and citrate in maternal milk. Objective measurements for established lactation, including 3-hourly pumping and 24-hour milk production, together with pre-feed to post-feed milk fat changes (a useful indicator of the available milk removed by the infant) have been outlined. Considered together with the parameters describing normal function, this information provides a preliminary objective framework for the assessment of human lactation.