A 28 year-old homosexual man had one month history of intermittent high fever, nonproductive cough and progressive shortness of breath. He not only had immunity deficits, with decrease CD4 cells decreased CD8 cells and inverted CD4/CD8 ratio, but also presented with evidence of human immunodeficiency virus infection (positive ELISA antibody tests and Western blot tests). Chest X-ray showed diffuse pulmonary infiltration. The arterial blood gases revealed hypoxemia. The PaO2 was 69 mmHg. Spirometry showed FVC 2.28 L (45% predicted), FEV1 2.21 L (49% predicted), FEV1/FVC 93%, and MMEF 4.41 L/sec (90% predicted). The configuration of the Flow-Volume loop was consistent with a restrictive ventilatory defect. Transthoracic lung biopsy demonstrated pneumocystis carinii pneumonia (PCP). He had inadvertent steroid therapy and showed some clinical, pulmonary function and chest X-ray improvement before the diagnosis was established. Steroids might be as adjunctive therapy for a short period of time in treatment of PCP associated with acquired immunodeficiency syndrome (AIDS) at respiratory failure.