We reviewed the problem of Segment IV in using left lobes from living related donors, in 18 left-lobe transplants performed on pediatric patients who ranged in age from 6.0 to 17.3 yr, and in body weight from 19.8 to 58.0 kg. The separate monitoring of oxygen saturation of hemoglobin in the liver sinusoid of segments, using a spectrophotometric technique, demonstrated a delay in re-oxygenation of Segment IV after the portal reflow, and revealed its return to comparable oxygenation with Segments II and III by the re-arterialization. Hemoglobin content, which was determined by the same technique, occasionally increased in Segment IV during the operation, implying sluggish microcirculation caused by inadequate hepatic venous drainage. These characteristic profiles on tissue oxygenation and hemodynamics in Segment IV should be considered when using left lobes as living related liver grafts.