1. Renal sympathetic nerve activity, ECG and parieto-occipital EEG were recorded in dogs anaesthetized with chloralose. The carotid sinus nerves were cut. Autocovariance functions and power spectra for these variables were computed. 2. During cooling of the vagus nerves, the integrated renal sympathetic activity exhibited rhythms which were correlated to the delta-theta rhythm of the EEG. This rhythm was also present with the vagus nerves functionally intact, but a cardiac rhythm was dominant. 3. Blood pressure-dependent neurones in the lower brain stem reticular formation have both cardiac and central cortical rhythms. This provides a hint that these neurones might be involved in the sympathetic tone generating network.