Increasing the supplies of methionine (Met), lysine (Lys), and histidine (His) at two levels of net energy of lactation (NEL) increased milk protein yield (MPY) and metabolisable protein (MP) efficiency (MP_Eff), reducing the efficiency (Eff) of these amino acids (AA) but increasing the Eff of the other essential AA (EAA). The increased MPY occurred with different changes in mammary net uptake (MGU) of AA in response to AA or NEL supplies. In addition, milk yield (MY) tended increased or increased in response to AA or NEL, respectively.