A 33-year-old man with a two-year history of asthma and sinusitis presented with wheezing, pleuritis, bilateral pleural effusions, and patchy basilar infiltrates on chest roentgenogram. Laboratory studies revealed peripheral blood eosinophilia, and pulmonary function studies showed an obstructive pattern which was bronchodilator responsive. Thoracocentesis yielded an acidotic exudative effusion with low glucose, low C3, eosinophilia, and a markedly increased rheumatoid factor. Open lung biopsy revealed extensive eosinophilic interstitial pneumonitis with necrotizing eosinophilic vasculitis. Although pleural effusions are present in 29 percent of Churg-Strauss patients, these effusions have not been well described. This report describes the pleural fluid findings in a case of Churg-Strauss syndrome.