Experiments were done to determine the central delay to inhibition of supraoptic neurosecretory neurones by carotid baroreceptors in chloralose-anaesthetised, paralysed cats. Fourteen out of 18 neurosecretory cells (identified by antidromic activation from the pituitary neural lobe) were tested for their response to inflation of the ipsilateral carotid sinus (prepared as a blind sac). This stimulus inhibited the spontaneous activity of 10 neurones, which were thus identified as putative vasopressin cells. Repetitive, precisely timed pressure pulses were delivered to the carotid sinus and used to construct post-stimulus histograms of this inhibition. The latency measured from the baroreceptor afferent barrage (recorded from the sinus nerve) to the onset of inhibition in supraoptic neurones was 251 +/- 58 ms (range 152-328, n = 10). The significance of this long latency for the neural pathways involved is discussed.