In early studies of humans, baroreflex sensitivity was found to be higher during sleep; however, subsequent observations, in several species, including humans, have been at variance with the original reports. Sleep and arousal are behavioral states, and it is difficult to accurately and repeatedly measure baroreflex sensitivity in behaving animals. However, pharmacologically immobilized (NMB) rats have apparently normal sleep-wakefulness cycles, and baroreflex gain can be measured directly in this preparation. Using the delta band of the EEG (EEG) as an index of sleep and arousal, and open-loop aortic depressor nerve (ADN) stimulation as a baroreflex input, we found that blood pressure (BP) level depended on arousal (r = -0.416; p<.0001), and BP baroreflex gain depended on BP level (r = .496; p<.0001), but that BP baroreflex gain was independent of arousal (r = 0.001; NS). Heart period (HP) was different: Although HP level depended on arousal (r = 0.352; p<.0001), HP baroreflex gain did not depend on HP level (r = 0.029; NS), and HP baroreflex gain increased with arousal (r =.315; p<.0001). A partial correlations analysis showed that the presence of the relationship between BP level and BP baroreflex gain probably attenuated the relationship between arousal and BP gain. The results are consistent (a) with physiological findings showing that arousal attenuates afferent transmission through the NTS, and enhances sympathoinhibition at the RVLM; (b) with observations in humans and animals showing increased cardiac baroreflex sensitivity during sleep, but little if any effect of sleep on blood pressure baroreflex sensitivity. The findings are relevant to all methods of baroreflex gain estimation that use heart period as the index of baroreflex activation.