We report two children, age 7 months and 5 years, who underwent surgery for congenital heart disease and developed persistent pleural effusions with elevated eosinophil counts. Given the elevation of eosinophil counts in both blood and pleural fluid of these patients, it was considered that an allergic response might have caused the persistent effusion. In both cases, the effusion resolved within 48 hours after treatment with corticosteroids was begun. It is possible that postoperative eosinophilic pleural effusion may represent a subgroup of effusions that are more likely to respond to treatment with corticosteroids.