BACKGROUND: Chrome eosinophilic pneumonia(CEP) is interstitial lung disease characterized by multiple infiltration on radiographic study, accumulation of eosinophils in the alveolar space and interstitium of the king, chronic persistent symptoms and possible relapse Acute eosinophilic pneumonia(AEP) is a recently described illness, characterized by rapid clinical course, acute respiratory insufficiency and no relapse. METHOD: To better characterize acute and chronic eosinophilic pneumonia, we studied the clinical arid laboratory features of 16 patients(AEP : 7 patients, CEP : 9 patients), which were clinico-pathohistologically diagnosed and not to be associated with organic disorders producing peripheral blood eosinophilia. RESULTS: The mean age was higher for patients with CEP than for patients with AEP (55.4+/-15.1 vs 24.6+/-7.9 years, p<0.05). High fever(above 38degrees C) was presented in all patients of AEP and in one patient(1l%) of CEP. All patients of AEP and eight patients(89%) of CFF showed bilateral pulmonary infiltrates, and 6 patients(86%) of AEP arid 2 patients(22%) of CEP showed pleural effusion in chest radiograph. The mean white blood cell count of AEP and CEP were 17,186/mm(3) and 12,867/mm(3), respectively. The mean peripheral blood cell eosinophil count of AEP and CEP were 939/mm(3) and 2,104/mm(3), respectively. The mean eosinophil fraction of BAL fluid of AEP and CEP were 32.4% (range: 18-47%) and 35.8%(range: 15.3-48.2%), respectively. The mean PaO2 was lower for patients with AEP than for patients with (SEP (44.1+/-15.5 vs. 62.7+/-6.9mmHg, p<0.05). All patients of AEP and (SEP were initially treated with antibiotics. All patients of CEP and one patients of AEP were finally required systemic steroid therapy. 6 patients of AEP were improved without steroid therapy. Relapse was observed in 3 patients(33%) of CEP. CONCLUISON: Compair with of chronic eosinophilic pneumonia, acute eosinophilic pneumonia was characterized by relatively young age, acute onset, high fever, severe hypoxemia, diffuse pulmonary infiltrates with pleural effusion, steroid therapy is effective but spontaneous improvement with conservative therapy was frequent.