We report five patients with chest roentgenograms showing peripheral infiltrates similar to that described for chronic eosinophilic pneumonia (CEP). While lung biopsy specimens (transbronchial and open in two and transbronchial only in three cases) revealed typical changes of bronchiolitis obliterans organizing pneumonia (BOOP) as the predominant finding in all cases, two cases had changes consistent with a resolving CEP. We speculate that (1) it may be common for BOOP to present with peripheral infiltrates, (2) chest roentgenograms showing peripheral infiltrates are not diagnostic of any specific entity, (3) idiopathic BOOP may represent the evolution of untreated CEP, (4) a lung biopsy may be a more appropriate initial approach than the therapeutic trial of corticosteroids when peripheral infiltrates of unknown origin are present, and (5) transbronchial biopsy may be adequate to establish a working clinical diagnosis of BOOP.