The structural rearrangement of human sheathed capillaries in congestive splenomegaly with hypersplenism has been evaluated by histometric analysis. In abnormal spleens the external diameter and the wall thickness were decreased, while the internal diameter was increased. Moreover, the total length and the absolute number of sheathed capillaries were increased, though not to the same high degree as the volume of the whole red pulp. Thus, in addition to the well-known changes of the sinuses, also the terminal arterial passages appear to participate in the morphological rearrangement of the red pulp in congestive splenomegaly.