Forty-three patients known to have systemic lupus erythematosus (SLE) underwent pulmonary function evaluation. Pulmonary dysfunction was noted in 38 patients (88%). The most common abnormality was an impairment in diffusing capacity, present in 31 patients (72%), while reduction in lung volumes was present in 21 patients (49%), hypoxia in 19 patients (44%), and airways obstruction in 4 patients (9%). When compared to pulmonary symptoms and signs and chest roentgenogram, the pulmonary function tests were the most sensitive means of uncovering pulmonary involvement in SLE. No correlation was found in either the classification or severity of the pulmonary function abnormality when compared with other measures of lupus activity, such as serology, immune complexes in skin biopsy, and renal biopsy.