The authors report on the use of intrapleural instillation of urokinase in the treatment of loculated pleural effusions in two pediatric patients. Urokinase helps to lyse fibrin by converting plasminogen to plasmin. The intrapleural instillation of urokinase is safe and effective for promoting drainage of loculated intrapleural effusions, and it proved a useful option in the treatment of persistent loculations.