Human leg lymphatics contract spontaneously, rhythmically propelling lymph. This intrinsic property regulates the fluid environment in the intercellular space in skin, connective tissue, and perivascular spaces. The pressures generated by lymphatic contractions constitute the main force for lymph flow. This mechanism is of utmost importance during night rest, anesthesia, and immobilization, as well as in those with damaged peripheral motor neurons. All supporting forces are only secondary to those created by spontaneous lymphatic contractions. The intrinsically regulated lymph flow depends on tissue fluid and lymph production rate. The transport capacity of lymphatics adjusts to the fluid load. Under physiological conditions, limb activity and position only slightly change lymph flow. In obstructive lymphedema, high lymph pressures can be observed. They are usually generated by leg muscle contraction, whereas the spontaneous contractility of lymphatics becomes ineffective in lymph transport because of low generated pressures and lymphatic valve insufficiency. The knowledge of lymph flow in normal and lymphedematou limbs will be useful in the derivation of rational treatments for lymphedema.