With the aim of contributing to a better understanding of the haemolytic function of the spleen, a morphologic and morphometric study of this organ fixed by arterial perfusion was performed in nine patients with hereditary spherocytosis (HS), three with autoimmune haemolytic anaemia (AHA) and six with Hodgkin's disease without splenic involvement (controls). The spleen weight in HS and AHA (621 +/- 429 g, mean +/- SD) was significantly increased with respect to controls (168 +/- 36 g) (P = 0.003). In HS the red cell retention in the cords of Billroth was significantly increased (203 +/- 68 per 10(4) microns 2) with respect to the cases with AHA (93 +/- 35 per 10(4) microns 2) and to the controls (57 +/- 28 per 10(4) microns 2) (P = 0.004). In HS and AHA the number of macrophages per 10(4) microns 2 of red pulp was significantly increased (5.41 +/- 1.10 and 7.52 +/- 2.91, respectively) with respect to the controls (3.25 +/- 0.58) (P less than 0.003). There was no statistically significant difference between the number of macrophages in HS and AHA. The transmission (TEM) and scanning electron microscopy (SEM) studies demonstrated predominantly red cell retention in the cords of HS spleens, red cell phagocytosis by cordal macrophages in AHA spleens and in a lesser intensity in HS spleens, and phagocytosis of haematic corpuscles by sinus endothelial cells (SEC) in the cases of HS. These quantitative studies allow a better understanding of splenic red cell destruction in haemolytic syndromes.