We report a novel mutation in the alpha2-globin gene, codon 35 (T-->C), detected in two unrelated Portuguese families. This mutation gives rise to a previously undescribed hemoglobin (Hb) variant, which we named Hb Evora. This variant seems to be responsible for the alpha-thalassemia phenotype present in its carriers. It cannot be detected by conventional laboratory techniques, probably because of its highly unstable nature.