Seventy-one patients who presented to the emergency room with acute asthma were evaluated to determine the relationship between common clinical signs and spirometric and transcutaneous arterial oxygen saturation (SaO2) measurements. Prior to treatment, a physical examination was performed, a clinical score assigned, and pulmonary function and SaO2 were measured. Although forced expiratory volume in 1 second (FEV1) and SaO2 had strong correlation with the overall clinical score (r2 = .47, .49 respectively), many patients with low clinical scores and apparent mild clinical disease had low FEV1 values (as low as 20% predicted). Of the individual components of the clinical score (ie, heart rate, respiratory rate, pulsus paradoxus, accessory muscle use, dyspnea, and wheezing), the degree of accessory muscle use correlated most closely with lung function followed by the degree of dyspnea and wheezing. Similarly, the degree of accessory muscle use correlated most closely with SaO2 followed by dyspnea and respiratory rate. Significant correlation (r2 = .59) was found between SaO2 and FEV1, although the range of SaO2 value for a given FEV1 was wide and some patients with low FEV1 values had normal SaO2 values. These results show that although clinically apparent severe disease and hypoxemia were always associated with low FEV1, their absence does not exclude the presence of airflow obstruction. It is concluded that for the optimal evaluation of acute asthma in children in the emergency room, clinical evaluation should be used in conjunction with objective laboratory measurements.