Results are reported of studies of the hemoglobin from one member of a Canadian family with a mild erythrocytosis. This variant, which accounted for about 40% of the hemoglobin, could be separated from Hb A and Hb A2 by cation-exchange chromatography. Micro methodology allowed the characterization of a Leu----Val replacement at position beta 96(FG3). Hb Regina has an increased oxygen affinity, which adequately explains the hematological observations.