The purpose of the present study was to evaluate the response of genioglossus muscle (GG) to bolus injection of aminophvlline (AP). Adult rats were anesthetized with urethane. Electromyograms (EMG) of the GG and the diaphragm (Dia) were observed. Blood pressure was monitored. GG EMG increased to 144% (p＜.0.01) and Dia EMG enhanced to 111% in response to 4 mg/kg of AP. With high dose of AP treatment (32 mg/kg b.w.), GG EMG increased to 188% (p＜0.01) while Dia EMG argumented to 122% (p＜0.01). After peak response, Dia activity was gradually recovered to normal level. Yet, GG EMG was still higher than that of control 30 minutes alter high dose of AP treatment. These results indicate that Dia and GG activities were enhanced by AP and that enhancement of GG response is much more than that of the Dia.