Single unit responses to tone pips (200 ms duration) or clicks were studied in the inferior colliculus of anaesthetized guinea-pigs. In all, 360 neurons were investigated. The tonotopic organization of neurons in the inferior colliculus and shapes of the threshold tuning curves were comparable with the data known in other laboratory animals. The majority of neurons (83.5 percent) displayed a tonic response to tonal stimuli, the remaining 16.5 percent of units responded with a typical "on" reaction at the beginning of the stimulus. The spike-intensity functions of 50 percent of neurons were of the non-monotonic type, the saturation of response was observed usually at 20-30 dB above the threshold. Monaural stimulation of the contralateral ear evoked an excitatory response in all cases; ipsilateral ear stimulation exerted an excitatory response in 61.8 percent of neurons, an inhibitory response in 17.6 percent of neurons and for 20.6 percent of units ipsilateral ear stimulation was uneffective. The occurrence of neuronal responses to stimuli with an interaural time delay or intensity differences was also investigated.