Diagnostic ultrasound imaging of the breast has been limited principally to the abnormal, non-lactating breast. Due to the rapid improvement of imaging technology, high-resolution ultrasound images can now be obtained of the lactating breast. Ultrasound scanning techniques, however, require modifications to accommodate the breast changes that occur in lactation. Furthermore, the function of the breast with regard to milk ejection can be assessed with ultrasound by identification of milk duct dilation and milk flow. At milk ejection, the echogenic duct walls expand as milk flows forward towards the nipple. Milk flow appears as echogenic foci rapidly moving within the milk duct. This paper provides a detailed description of the ultrasound technique used for the detection and reviews nuances associated with the procedure.