The perfusion of human donor livers was studied during organ retrieval using laser Doppler flowmetry to assess the microcirculatory alteration caused by fatty infiltration (steatosis). Using a multichannel laser Doppler flowmeter, we measured the hepatic perfusion as flux units in 21 liver donors, eight of which were macroscopically fatty. Perfusion was recorded continuously for 2 minutes from two sites on each lobe at the beginning of organ retrieval, after the vascular dissection, and during sequential occlusion of the hepatic artery and portal vein. Mean flux value and SEM were calculated, and paired Student's t test was used for comparison between stages of perfusion. Multiple ANOVA was used to determine whether factors other than the normal or fatty parenchyma influenced the perfusion measurements. Mobilization of the graft did not affect parenchymal perfusion. Perfusion was significantly (P < 0.001) and rapidly reduced with hepatic artery or portal vein occlusion in both groups. Macroscopically steatotic livers (n = 8) had diminished microcirculation compared with normal livers (n = 13) (125 ± 18 v 252 ± 24 flux units; P = 0.002). Donors receiving inotropes (n = 10) had a lower mean perfusion rate (150 ± 20 v 252 ± 29 flux units; P = 0.026), but this effect was found in both the normal and steatotic groups with no interaction (ANOVA; P = 0.658). Steatosis diminishes the tissue perfusion in human liver grafts. Laser Doppler flowmetry may help identify grafts with a compromised microcirculation.