The reticuloendothelial system function, especially phagocytic activity, and hepatocyte function were investigated in dogs undergoing an orthotopic liver transplantation. The donor's phagocytic index, measured by a lipid emulsion test, was higher in the Survivor group which survived more than 3 days after transplantation (0.063 +/- 0.008 vs 0.024 +/- 0.002; mean +/- standard error of the mean (SEM), P < 0.01). There was a statistically significant difference in the phagocytic index between the survivor and nonsurvivor groups. However, the hepatocyte function at an early phase after transplantation, indicated by the arterial ketone body ratio, hepaplastin test and lecithin cholesterol acyltransferase level, did not distinguish the Survivor group from the Nonsurvivor group at all. In the survivor group, the hepaplastin test and the lecithin cholesterol acyltransferase level were significantly decreased after liver transplantation, namely from 155 +/- 15% to 58 +/- 5% and from 57 +/- 12 unit/ml to 19 +/- 1 unit/ml on the 2nd day after transplantation (P < 0.01, P < 0.05), respectively. On the other hand, the reticuloendothelial system (RES) function, as estimated by the phagocytic index and serum complement activity (CH 50), demonstrated no change throughout the experimental period. The present study therefore demonstrated that the operative results might be affected by the phagocytic activity.