The cardio-respiratory effects of carotid body (CB) and aortic body (AB) stimulation are well described1. Superior laryngeal nerve (SLN) paraganglia have been shown to be structurally similar to the glomus cells of the CB and are excited by both cyanide and hypoxia in vitro2. The aim of the present study was to elucidate the reflex action of these paraganglia on breathing and the circulation. Experiments were carried out on Wistar rats (body mass: 272 ± 38 g, n=6) anaesthetised with 20% urethane (1.5g kg-1 i.p.). The right external jugular vein was cannulated for administration of sodium cyanide (NaCN) in normal saline. Both SLNs were cut close to the larynx but preserving the region of bifurcation, an area that reliably contains glomus tissue, with the free ends placed in small 20μl tissue baths containing Tyrode’s solution. The CB and AB were first stimulated by injecting 20-40μl NaCN through the pre-filled jugular vein cannula. SLN paraganglia were then selectively stimulated by adding 10μl of 0.1mg ml-1 NaCN to the tissue baths. These two tests were then carried out simultaneously to assess potential interaction between the reflex responses. At the end of the experiment both SLNs were cut and the tests repeated to ensure that responses were due to activation of the SLNs and not NaCN leakage from the bath. The initial mean cardiorespiratory values were: respiratory frequency, 86 ± 23 breaths min-1; heart rate, 415 ± 40 beats min-1; mean arterial pressure, 93 ± 14 mmHg; hindlimb conductance 0.012 ± 0.007 ml min-1mmHg-1; arterial blood pH 7.41 ± 0.02; PO2, 95 ± 13 mmHg; PCO2, 38 ± 2 mmHg; haematocrit, 50 ± 4%. Intra-cardiac injection of NaCN caused tachypnoea (increasing respiratory frequency by 48 ± 29%) and hindlimb vasodilatation. The response resembled that previously reported in the saffan anaesthetised rat3. Of interest, the SLN paraganglia had no significant effect on breathing or heart rate but caused a significant hindlimb conductance increase and a greater vasodepressor response (-10 ± 6%) compared to stimulation of all the other chemoreceptor sites. The effect on hindlimb conductance was additive when SLN stimulation was conducted at the same time as systemic cyanide injection. Further experiments are required to determine whether the SLN chemoreflex evokes a pattern consistent with a hypothalamic defence response, Sherrington’s pseudoaffective response or a thermoregulatory response. All values reported are mean ± S.D.