Free amino acid concentrations in erythrocytes obtained from children with hereditary spherocytosis were measured before and after splenectomy. The concentrations of about half of the free amino acids were elevated before splenectomy, and this elevation may be due in part to increased numbers of reticulocytes. After splenectomy, however, the concentration of erythrocyte amino acids was not normalized and that of six to eight amino acids was still elevated. This elevation after splenectomy may be due to spherocytes themselves