An abnormal, fast moving hemoglobin was noted in a 34-yr-old male patient living in Legnano (northern Italy) affected with renal failure and iron deficiency anemia, not related to the presence of the Hb variant. Structural studies have demonstrated a previously undescribed amino acid substitution, alpha 141 Arg replaced by Leu. This new variant has been named Hb Legnano, and is characterized by an increased oxygen affinity and a low cooperativity, at least as far as preliminary functional studies carried out on whole blood have indicated. Family studies are reported: three other heterozygous carriers were observed among the relatives of the propositus, all showing a mild polycythemia which, however, does not seem to produce appreciable clinical consequences.