We made small injections of horseradish peroxidase into the medial superior olivary nucleus (MSO) of gerbils in order to examine the sources of input into that nucleus. As previously described, the MSO receives inputs from neurons in the rostral part of both anteroventral cochlear nuclei. In addition, we found evidence for a projection from the ipsilateral lateral nucleus of the trapezoid body (LNTB). Our results are also compatible with previous reports that the medical nucleus of the trapezoid body (NMTB) projects to the MSO. It is likely that these projections into the MSO from the LNTB and MNTB are sources of inhibitory synaptic inputs.