A 32-year-old Sicilian man had marked erythrocytosis (Hb = 23.0 g/dl, RBC = 10.5 x 10(12)/l, MCV = 71 fl, Hct = 84-92%, a 4.5 times increase in total erythropoies) and saphenous system varices, without other clinical abnormalities. By Hb electrophoresis, an abnormal Hb migrating slightly more anodally than Hb A was found. HbA0 was almost completely absent. The abnormal Hb was recognized to be Hb Malmö [beta 97 (FG4) His-Gln], a human Hb variant with greatly increased oxygen affinity. The patient was also a carrier of the beta-thalassemia trait. The father of the propositus was a heterozygous carrier of Hb Malmö (about 40% of total Hb), while his mother had only a beta-thalassemia condition. This is the first reported case of double heterozygosity for both Hb Malmö and beta-thalassemia, thus producing complete absence of normal Hb.