The principal clinical pulmonary findings were extracted from University of Michigan Hospital records of 390 patients with scleroderma. Dyspnea was the most frequent symptom and strongly correlated with pulmonary fibrosis and with decreased vital capacity (FVC) and CO diffusing capacity (DLCO). The mean value for FVC was 84% of the predicted normal for 326 patients, and that of the initial DLCO 56.8% of the predicted normal (323 patients). Pulmonary fibrosis was diagnosed on first chest X-ray in’80 of 382 patients. An additional 48 patients developed fibrosis detected on subsequent X-rays.Analyses were performed to determine whether the deterioration of pulmonary function over time was less for scleroderma patients who were adequately treated with potassium p-aminobenzoate (KPAB) than for those inadequately or never treated with KPAB, The average decrease for both FVC and DLCO was found to be less for KPAB-treated patients. However, only in the case of vital capacity was the difference significant. In the presence of radiological evidence of pulmonary fibrosis FVC decreased more rapidly (p = 0.002), but the decline in DLCO was not affected. When adjusting for the presence or absence of fibrosis the average slopes of the logarithm of vital capacity were significantly less negative (p = 0.003) for patients on KPA