Blood from 5 patients suffering from hereditary spherocytosis (HS) was stored in acid-citrate-dextrose anticoagulant at 4 degrees C for up to 6 weeks. The erythrocyte morphology and susceptibility to lysis by phospholipase C (Bacillus cereus) were examined at 2-weekly intervals and compared with erythrocytes from 6 different donations of stored normal blood. the hereditary spherocytes went through essentially the same series of morphological changes as did normal erythrocytes. Fresh hereditary spherocytes were very resistant to lysis by phospholipase C, but, like normal erythrocytes, became progressively more susceptible to lysis upon storage. In terms of erythrocyte morphological changes and development of susceptibility to lysis by the enzyme, blood from HS patients aged less rapidly than did normal blood. Splenectomy appeared to have no marked effect on the storage properties of blood from these patients as indicated by erythrocyte morphology and susceptibility to lysis by phospholipase C.