The P-50 value, a marker for the behavior of the oxygen dissociation curve (ODC) and values of 2,3-diphosphoglyceric acid (2,3-DPG), blood gases and acid base parameters (pH, PCO2, actual HCO3-, base excess, PO2, SO2) and erythrocyte parameters (the number of erythrocyte, hematocrit and hemoglobin values) that are known to effect P-50, were measured before and after ultrasound (US) exposure to examine the effect of pulsed US beams on the ODC of human erythrocytes. Venous blood samples taken from healthy subjects were sonicated at 0degreesC for 30 min by pulsed US beams with a constant frequency of 5 MHz. Experiments showed that the values of pH, actual HCO3-, standard HCO3- base excess, 2,3-DPG and P-50 were changed considerably by pulsed US. Furthermore, correlation calculations were made to find out the relation between the P-50 values and the other parameters. As a result, a significant relation was found between P-50 values and the values of pH, actual HCO3-, PO2, SO2 and 2,3-DPG. In conclusion, we can express that a highly significant increase occurs in P-50 value of venous blood after a pulsed US exposure at a constant frequency of 5 MHz for 30 min under in vitro conditions at 0degreesC. That is hemoglobin becomes suitable for deoxy (tense structure) conformation when blood affinity of O-2 is low. It means that hemoglobin becomes convenient for proton (H+) and CO2 binding. (E-mail: email@example.com) (C) 2002 World Federation for Ultrasound in Medicine Biology.