An analysis of the reflex output of a motoneuron pool in response to a Ia-afferent input is presented. The analysis is based upon a model of the motoneuron pool which includes the subthreshold behavior of motoneurons (integration of synaptic inputs) and the statistical distribution of the motoneurons according to their resting conductance. The latter feature allows for the orderly recruitment of the motoneurons in the order of low resting conductance to high resting conductance. The number of active motoneurons (i.e. the excitation level) is determined by the balance of the excitatory and inhibitory conductances acting on the pool. The reflex output in response to a Ia-EPSP is computed at various excitation levels and with different amounts of presynaptic inhibition. The reflex output is the same for a given excitation level, regardless of the mixture of excitatory and inhibitory postsynaptic conductances used to produce that excitation level. In contrast, presynaptic inhibition markedly affects the relation between reflex output and excitation level.