Respiratory afferent stimulation can elicit increases in respiratory motor output that outlast the period of stimulation by seconds to minutes (short-term potentiation, STP). This study examined the potential contribution of spinal mechanisms to STP in anesthetized, vagotomized, paralyzed rats. Following C₁ spinal cord transection, stimulus trains (100 Hz, 5-60 s) of the C₁-C₂ lateral funiculus elicited STP of phrenic nerve activity that peaked several seconds post stimulation. Intracellular recording revealed that individual phrenic motoneurons exhibited one of three different responses to stimulation: 1) depolarization that peaked several seconds post stimulation, 2) depolarization during stimulation and then exponential repolarization following stimulation, and 3) bistable behavior in which motoneurons depolarized to a new, relatively stable level that was maintained following stimulus termination. During the STP, EPSPs elicited by single stimulus pulses were larger and longer. In conclusion, repetitive activation of the descending inputs to phrenic motoneurons causes a short-lasting depolarization of phrenic motoneurons, and augmentation of EPSPs, consistent with a contribution to STP.