One hundred children suffering from acute asthma were studied. Both pulsus paradoxus (PP) and CO2 pressure (PCO2) of the arterialized blood sample were measured in each child. The correlation between the PP and the PCO2 was not statistically significant when the latter was less than 35 mmHg (p less than 0.05). When the PCO2 was equal or higher than 35 mmHg, a directly proportional as well as statistically significant relationship with PP was found (p less than 0.00001). PP is proposed as an indirect indicator of the PCO2 on patients suffering from acute asthma, when the necessary equipment to measure the PCO2 is not available.