Fractionations are 20- to 100-ms pauses in diaphragm activity that occur spontaneously during rapid-eye-movement (REM) sleep, sometimes in association with pontogeniculooccipital (PGO) waves. Auditory stimuli can elicit fractionations or PGO waves during REM sleep, non-REM (NREM) sleep, and waking; however, their interrelationship has not been investigated. To determine whether the two phenomena are produced by a common phasic-event generator in REM sleep, we examined PGO waves and fractionations that were elicited by auditory stimuli (tones) presented to freely behaving cats across states. Tones elicited PGO waves and two types of fractionations: short-latency fractionation responses (SFRs; 10- to 60-ms latencies) and long-latency fractionation responses (LFRs; 60- to 120-ms latencies). Both a PGO wave and a SFR were elicited in 60-70% of trials across states, but each could be elicited alone. The latencies and durations of elicited SFRs were similar across states, but the latencies of elicited PGO waves in REM sleep (mean 62.5 ms) were significantly longer than in waking or NREM sleep. Elicited SFRs consistently occur with shorter latencies than do PGO waves, in contrast to spontaneous fractionations, which have a variable relationship to PGO waves and usually occur 10-40 ms after the onset of the PGO wave. The LFR then, elicited most frequently during REM sleep, resembles a spontaneous fractionation in its temporal relationship to the PGO wave and may reflect the bias toward motoneuronal inhibition characterizing REM sleep but not NREM sleep or waking. We conclude that, although PGO waves and SFRs share some features, like LFRs they probably are generated by different neuronal populations. In three cats there was no correlation between PGO waves and fractionations, whereas in one cat they were associated in REM sleep (LFRs and SFRs) and waking (SFRs only). Thus the majority of evidence argues against the existence of a common phasic-event generator in REM sleep.