The usefulness and limitations of various laboratory examinations used in the evaluation of respiratory impairment were discussed. Spirometry provided one of the most widely used objective tests of pulmonary function. However, the technique required a great deal of subject cooperation and coaching. There was a wide range of intersubject and intrasubject variability in spirometric values. Factors such as age, height, sex, and race influenced spirometric values. Testing of the diffusing capacity of the lung were useful in the evaluation of many infiltrative diseases, in which spirometric values may be relatively well preserved. Although diffusion capacity tests provided results which were imprecise and even less reproducible than spirometry, they were noninvasive and provided information supplemental to spirometry. Determination of arterial blood gases provided a relatively simple method for indirect estimation of the adequate exchange. The sampling of arterial blood from a peripheral artery caused only minor discomfort and was associated with minimal risks. Exercise testing added useful information when more than one organ system was impaired and in cases of borderline pulmonary impairment, but was not considered necessary as a screening procedure in disability evaluations, if spirometry of arterial blood gases, and when applicable, diffusing capacity were performed. Lung impairment was difficult to quantitate due to the wide range of intersubject variability during normal function. Remaining maximal capacity lung function was more accurately determinable than amount of functional impairment. Disability evaluations were focused on determining the remaining functional capacity in relation to the demands of work to be performed. Estimating job demands, although problematic, was considered essential in determining whether an individual was disabled. The criteria currently in use or recommended by authorities for disability evaluations were summarized. Recommended guidelines for disability evaluation were provided. The author concludes that the final determination of disability depends upon the judgement of experienced physicians and claims adjudicators.