Lumbricus spencer, which has been used as an antipyretic in Chinese and Japanese folk medicine and whose antipyretic components are identified to be eicosatetraenoic acid and eicosapentaenoic acid, was given orally in a single dose of 500 mg to febrile patients with acetylsalicylic acid-induced asthma (AIA) in placebo-controlled design. The antipyretic effect of Lumbricus spencer was observed with no exacerbation of asthmatic symptoms. Single oral administration of 500 mg of Lumbricus spencer did not affect the respiratory functions in the patients. Moreover, there were no significant changes in symptom scores and airway lability as measured by daily variations in peak expiratory flow after one week administration of 1500 mg/d of Lumbricus spencer. This pilot study suggests that Lumbricus spencer can be administered safely to febrile patients with AIA without bronchospasm.