A simple mathematical model of the carotid body chemoreceptor response is presented. The model assumes that the static chemoreceptor characteristic depends on oxygen saturation in the arterial blood and on CO 2 arterial concentration. The values of O 2 saturation and of CO 2 concentration are computed, from pressure, using blood dissociation curves, which include both the Bohr and Haldane effects. Moreover, the O 2 -CO 2 static responses interact via a multiplicative term followed by an upper saturation. The dynamic response includes a term depending on the time derivative of CO 2 concentration and a low-pass filter, which accounts for the time required to reach the steady state level. With a suitable choice of its parameters, the model reproduces the carotid chemoreceptor response under a variety of combined O 2 and CO 2 stimuli, both in steady state conditions and in the transient period following acute CO 2 or O 2 pressure changes. In particular, simulations show that if two hypercapnic stimuli are given in rapid succession, the response to the second stimulus is weaker than the first. Moreover, during transient conditions the effect of CO 2 pressure changes prevail over the effect of O 2 changes, due to the intrinsic derivative component of the response to CO 2 . In conclusion, the model allows present knowledge about chemoreceptor activity to be summarized in a single theoretical framework. In perspective, it may be used as an afferent block within large-scale models of the overall cardio-respiratory control system.