Haemoglobinopathies are the world's most frequently found monogenic disorders. In the cases with high oxygen affinity, the decrease in the liberation of the oxygen determines a secondary erythrocytosis. In this work, we present 17 unrelated families of Caucasian race and of Spanish origin, with ten variants of haemoglobin or haemoglobinopathies with high oxygen affinity which were diagnosed in our laboratory. Of the ten haemoglobinopathies, in four (the Hb San Diego, the Hb Johnstown, the Hb Malmö and the Hb Columbia-Missouri), the change of amino acid affects zones of the contact alpha(1)beta(2); in two variants (the Hb Strasbourg and the Hb Syracuse), it affects the unions with 2,3-DPG in the central cavity; in the other two (the Hb Badalona and the Hb La Coruña), the cavity of contact with the group haem is affected; in one (Hb Bethesda), it affects the zone of contact alpha(1)beta(1;) and in one (Hb Olympia), the position 20 of the chain in the helix B in the surface of the protein is affected. In all cases, the change of amino acid, though of different form, facilitates that the quaternary structure of the haemoglobin becomes stable in its relaxed configuration so the transfer of oxygen and the P(50) value are decreased. All cases were sent to our laboratory because of shown erythrocytosis. In the majority of them, the diagnosis was done during an analysis of routine or for being relatives of the first ones.