The Kölliker-Fuse region (KF) and the lateral parabrachial nucleus (LPBN) have been implicated in the maintenance of cardiorespiratory control. Here, we evaluated the involvement of the KF region and the LPBN in cardiorespiratory responses elicited by chemoreceptor activation in unanesthetized rats. Male Wistar rats (280-330g, n=5-9/group) with bilateral stainless steel guide-cannulas implanted in the KF region or the LPBN were used. Injection of muscimol (100 and 200 pmol/100 nl) in the KF decreased resting ventilation (1140 ± 68 and 978 ± 100, vs. saline: 1436 ± 155 ml/kg/min), without changing mean arterial pressure (MAP) and heart rate (HR). Bilateral injection of the GABA-A antagonist bicuculline (1 nmol/100 nl) in the KF blocked the inhibitory effect on ventilation (1418 ± 138, vs. muscimol: 978 ± 100 ml/kg/min) elicited by muscimol. Muscimol injection in the KF reduced the increase in ventilation produced by hypoxia (8% O₂) (1827 ± 61, vs. saline: 3179 ± 325 ml/kg/min) or hypercapnia (7% CO₂) (1488 ± 277, vs. saline: 3539 ± 374 ml/kg/min) in unanesthetized rats. Bilateral injection of bicuculline in the KF blocked the decrease in ventilation produced by muscimol in the KF during peripheral or central chemoreflex activation. Bilateral injection of muscimol in the LPBN did not change resting ventilation or the increase in ventilation elicited by hypoxia or hypercapnia. The results of the present study suggest that the KF region, but not LPBN, have mechanisms to control ventilation in resting, hypoxic or hypercapnic conditions in unanesthetized rats.