Hepatic artery thrombosis and early acute rejection are severe complications of orthotopic liver transplantation (OLT). Their rapid detection is most desirable. The purpose of this study was to assess the usefulness of monitoring hepatic artery (HABF) and portal vein (PVBF) blood flows during the first week after OLT. At the end of operation, microprobes were sutured to the vessels, and their connecting tubes were externalized and connected to a pulsed Doppler flowmeter operating at 8 MHz. In 10 patients (ages ranged from 2 to 54 years) of 106, measurements of HABF and PVBF were done during alternative clamping of both vessels and before and after abdominal closure, every 12 hours during 7 days, and at day 7, before and after a 150 gm carbohydrate meal. At day 7 the probes were pulled out by gentle traction without complication, and all patients were allowed to go home. Reciprocal increase of flow during selective clamping was only observed for HABF (+45.8% +/- 47.6%; p less than 0.01). Abdominal closure decreased both HABF and PVBF by 13.8%, p less than 0.01, and 26%, p less than 0.05, respectively. In seven cases no significant variation of HABF and PVBF was observed during 7 days. In two patients with histologically confirmed early acute rejection, a marked decrease of diastolic HABF, without modification in PVBF, was the first manifestation and was rapidly corrected by boluses of steroids. In one patient disappearance of systolic and diastolic HABF led us to diagnose an arterial obliteration caused by a plicature, which was successfully surgically treated in the emergency department. In all patients, after oral ingestion of the carbohydrate meal, and only after this type of diet, a significant and deep decrease (-87%, p less than 0.001) of HABF was observed between 7 and 120 minutes without any change in PVBF. Such an effect was not observed in control patients. We conclude that this Doppler flowmetric technique with implantable microprobes is useful for rapid diagnosis of and strategy in treating early complications and is a new tool for pathophysiologic study of OLT consequences.