Hemoglobin Hotel-Dieu was detected by isoelectric focusing during investigation of a patient who had erythrocytosis. This variant migrates on cellulose acetate electrophoresis to a cathodic position relative to Hb F. In hemoglobin Hotel-Dieu, aspartic acid is substituted by glycine in position 99 of theβchain. As in other abnormal hemoglobins in which substitution of this residue has occured, Hb Hotel-Dieu exhibits a high oxygen affinity and is associated with familial erythrocytosis.