Effects of electrical and chemical stimulation of the dorsal and ventral areas of the nucleus raphe dorsalis (dNRD and vNRD) on genioglossus and diaphragm activities were observed in 48 urethane-anaesthetized and vagotomized rabbits. (1) Long train electrical stimulation at the dNRD facilitated genioglossus and diaphragm activities. (2) Long train electrical stimulation delivered to the vNRD excited genioglossus activity but inhibited diaphragm activity. (3) Effects of microinjection of glutamate at the dNRD and vNRD were similar to the effects of electrical stimulation. The above results suggest that excitation of nucleus raphe dorsalis (NRD) increases genioglossus activity and reduces upper airway resistance. The dNRD and vNRD play different roles in modulating diaphragm activity.