Despite the absence of lobulation, light microscopy of serial sections of the liver of brown trout, Salmo trutta fario, reveals that the stromal elements are spatially organized as venous–biliary–arteriolar tracts (VBAT), venous–arteriolar tracts (VAT), biliary–arteriolar tracts (BAT), venous–biliary tracts (VBT), biliary tracts (BT), arteriolar tracts (AT), and isolated veins. These components are not two- but three-dimensional entities, and the anatomical interrelationships among all entities are displayed. The VBAT, VAT, and VBT are considered portal tracts; the adjacent parenchymal zones are viewed as periportal areas. The veins emerging from those tracts are regarded as afferent, and related with periportal zones. The veins that do not communicate with the VBAT, VAT, or VBT are viewed as efferent. Only serial sectioning allows a definite recognition of afferent from efferent isolated veins. The morphometric study discloses that isolated veins occupy around 60% of the stromal areas. Nevertheless, the VBAT, VAT, and BT are also considerably important, occupying variable proportions of the stromal areas (8–12%). The VBT and BAT are less important in quantitative terms. No sexual diffences appear in either qualitative or quantitative terms. There is no structural support for an eventual macroorganization of hepatic tissues. It is suggested that the quantitative data can be useful, as standards for the normal hepatic architecture of brown trout. The paper emphasizes the importance of a general structural model for the fish liver and of the use of an internationally acceptable nomenclature. © 1995 Wiley-Liss, Inc.