OBJECTIVE To report on observations made in a group of patients with idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP) who were treated with interferon gamma-1b. Patients and Methods We reviewed the clinical records, radiological studies, and pulmonary function data of all patients treated with interferon gamma-1b between January 2000 and March 2002 at the Mayo Clinic in Rochester, Minn. Results Twenty-one patients (mean age, 68 years; range, 52-80 years) were treated with interferon gamma-1b for a mean duration of 8.2 months (range, 3-21 months). All patients had been diagnosed previously as having IPF/UIP based on clinical, pulmonary function, and chest highresolution computed tomographic scan criteria; 12 patients had also undergone video-assisted thoracoscopic surgical lung biopsy. Baseline pulmonary function data (mean ± SEM percent predicted) were as follows: total lung capacity, 57.3±2.5; vital capacity, 55.0±3.3; diffusing capacity of lung for carbon monoxide, 39.7±2.8; and forced expiratory volume in 1 second, 58.1±3.6. Only 1 patient showed symptomatic and functional improvement, and 7 discontinued treatment because of a perceived lack of benefit. Eleven patients (52%) died after a mean of 6.4 months of treatment, and follow-up pulmonary function data suggested continued worsening in all but 1 patient. Conclusion These observations do not support the use of interferon gamma-1b therapy for patients with advanced IPF/UIP.