The basis for the relationship between the discharges in the external cartized cats that were vagotomized, paralyzed, and artificially ventilated. Ive discharge (with the period of the cycle of phrenic nerve activity) is extrinsically imposed on central sympathetic networks by elements of the brainstem respiratory oscillator. However, a number of observations made in the present study contradict this view. First, changes in respiratory rate were accompanied by dramatic shifts in the phase relations between sympathetic and phrenic nerve discharge. Second, slow oscillations of sympathetic and phrenic nerve discharge were not always locked in a 1:1 relation. Third, the slow sympathetic rhythm persisted when respiratory rhythmicity disappeic components of sympathetic and phrenic nerve activity are generated by in