A previously healthy 54-year-old white man developed cough and dyspnea after inhaling dust. He was given a diagnosis of exacerbation of asthma on the basis of mild wheezing, but he failed to respond to bronchodilators. Two weeks later, a chest radiograph revealed a left pleural effusion. He was referred for evaluation. Examination indicated he was well developed and well nourished, with BP of 136/92 mm Hg and oxygen saturation of 96%. He had diminished breath sounds in the left hemithorax and dullness to percussion. There was no egophony or wheeze. Spirometry showed an FEV1 of 1.61 L (36%), an FVC of 2.57 L (47%), and an FEV1/FVC of 62.6%. CT scanning of the chest confirmed a large left pleural effusion with compressive atelectasis. His WBC count was 6,100/μL with 451 eosinophils (7.4%). Two thousand two hundred milliliters of viscous and chalky fluid was removed. Pleural fluid analysis showed the following values: pH, 7.08; protein, 11.9 g/dL; lactate dehydrogenase (LDH),2,714 IU/L (serum LDH, 196 IU/L); glucose, 7 mg/dL; triglycerides, 131 mg/dL (serum triglycerides, 182 mg/dL); WBC count, 17,200; and RBC count, 42,000. Cholesterol crystals were not seen. The supernatant remained cloudy after centrifuge. A cytotechnologist and microbiologist carefully reviewed the fluid and, after considerable analysis, found characteristic operculated eggs consistent with P westermani (Fig 1). Serum IgG enzyme-linked immunosorbent assay (ELISA) for P westermani measured 1:128 (positive titer ≥1:32). The patient was treated with praziquantel, 3,000 mg, po tid for 2 days. Because of persistent symptoms, he was retreated with praziquantel 2 weeks later. He also required a second thoracentesis. This time, the cholesterol was measured at 80 mg/dL, triglycerides 75 mg/dL, and LDH 4,590 IU/L, with 52% eosinophils on the fluid differential. He improved gradually and a subsequent chest radiograph showed minor linear scarring at the left base. His IgG ELISA to P westermani dropped to 1:16 approximately 16 months after initial treatment with praziquantel.