A new technique of segmental liver resection by use of intraoperative ultrasound (IOUS) and injection of methylen blue was evaluated in 15 sheep to study anatomical precision and alterations of the biochemical profile. The results were compared with those of a bisegmentectomy (n = 15) in which segmental boundaries were identified by IOUS alone. In a third group (n = 10) a sham operation (laparotomy without resection) was performed to study the intrahepatic vascular architecture of the liver by IOUS. The quality of the resections and of the ultrasound study was assessed by use of corrosion casts of the livers. The intrahepatic course of the liver veins and their confluence as well as the portal vein and its branches up to the segmental portal pedicles could be detected in all livers. Anatomically precise bisegmentectomies were achieved in 70% of IOUS combined with coloring of the segments versus only 27% in IOUS alone (p < .05). Biochemical and clinical parameters did not reveal any advantage of anatomically precise resection. The results show that intraoperative ultrasound is reliable in visualizing the intrahepatic anatomical characteristics of the liver, but it is imprecise in identifying segmental boundaries or in localizing a segment exactly. Anatomically precise liver resections are technically feasible by use of IOUS plus selective staining of the segments.