We have studied the action of deltamethrin on respiratory modulated hypoglossal motoneurons in a brain stem slice from newborn mice. Deltamethrin depolarized the hypoglossal motoneurons, increased the background synaptic noise and reduced the frequency and amplitude of current elicited action potentials. Deltamethrin transiently increased the frequency of the respiratory rhythm. Inspiratory potentials in hypoglossal motoneurons were decreased in amplitude and increased in duration. In conclusion, deltamethrin perturbs the respiratory output from the hypoglossal nucleus through postsynaptic actions on hypoglossal motoneurons and by affecting the inspiratory synaptic drive.