Abstract Portal venous flow (PVF) was serially monitored after pig liver transplantation (LTX) with the use of an implantable, miniature Doppler probe developed in our laboratory. Throughout the study period, the mean PVF in pigs that underwent LTX was significantly greater than that in pigs that were sham operated. For three animals with early graft failure secondary to primary nonfunction and for six that survived longer than 7 days, the mean PVF on postoperative day (POD) 1 was 18.7 ± 3.8 cm/s and 41.7 ± 11.2 cm/s, respectively (P < 0.05). For animals with acute cellular rejection (ACR), the mean PVF was 61.3 + 9.9 cm/s on POD 7 and 54.3 ± 6.38 cm/s on POD 14. These values were significantly higher than those for animals without ACR (P < 0.05). Moreover, the increase in PVF correlated well with the degree of ACR. The actual PVF volume was measured by ex vivo perfusion, which showed a clear correlation with the PVF velocity obtained with the implanted, miniature Doppler probe. We feel that the liver graft requires increased PVF volume after transplantation to facilitate functional recovery from damage to hepatocytes due to pres-ervation-reperfusion injury, and that ACR is also associated with an increased PVF. We conclude that monitoring the PVF in the early postoperative period after LTX is useful in the evaluation of graft function, particularly for predicting primary nonfunction and severity of ACR.