Summary 1. Auditory intemeurones originating in the metathoracic ganglion of females of the grasshopper Chorthippus biguttulus can be classified as local (SN), bisegmen- tal (BSN), T-shaped (TN) and ascending neurones (AN). A comparison of branching patterns and physiological properties indicates that auditory inter- neurones of C. biguttulus are homologous with those described for the locust. 2. Eighteen types of auditory neurones are morphologically characterized on the basis of Lucifer Yellow staining. All of them branch bilaterally in the metathoracic ganglion. Smooth dendrites, from which postsynaptic potentials (PSPs) can be recorded, predominate on the side ipsilateral to the soma. If 'beaded' branches exist, they predominate contralaterally. The ascending axon runs contralaterally to the soma, except in T-fibres. 3. Auditory receptors respond tonically. The dynamic range of their intensity- response curve covers 20-25 dB. Local, bisegmental and T-shaped neurones are most sensitive to stimulation ipsilateral to the soma. The responses of SN1 and TNI to white-noise stimuli are similar to those of receptors, while phasic-tonic responses are found in SN4, SN5, SN7 and BSN1. The bisegmental neurones receive side-dependent inhibition that corresponds to a 20-30dB attenuation. One local element (SN6) is predominantly inhibited by acoustic stimuli.