Parameters characterizing the hemoglobin oxygen affinity were determined in blood of 12 male patients suffering from arterial occlusive disease (AOD) of the legs and compared with data obtained earlier from healthy human subjects (controls). Due to a COHb content of 4.8% +/- 2.2% in the cigarette-smoking AOD patients, the standard oxygen dissociation curve (ODC) was left-shifted, the half-saturation pressure (P50) amounted to 24.8 +/- 1.7 mmHg (3.30 +/- 0.23 kPa), although the 2,3-diphosphoglycerate concentration was increased to 15.3 +/- 1.7 mumol/g Hb. Correcting the effects of elevated COHb shifts the P50 to 26.3 mmHg (3.5 kPa) and increases the steepness of the ODC (Hill's "n") from 2.79 +/- 0.27 to about 2.99, which is significantly different from controls. The Bohr coefficients after acidification of blood with lactic acid (BCLac) show high values at low oxygen saturations of hemoglobin (-0.50 +/- 0.04 in AOD patients, -0.32 +/- 0.04 in controls; P less than 0.05 at 10% SO2). The cause of the alterations in hemoglobin oxygen affinity may be a reduced mean erythrocyte age, but also the influence of unknown factors generated, e.g., from anaerobic muscle metabolism in AOD.