The equations describing the random displacement of the density interface and the associated velocity potentials in a constant depth, two-layer fluid with a rigid lid were solved to second order using an expansion technique analogous to that used to study random surface waves by Longuet-Higgins <1963> and Sharma and Dean <1979>. As expected, the first-order solutions represent a linear superposition of many waves with different amplitudes, wave numbers and frequencies. The second-order solutions describe the second-order wave-wave interactions. The solutions derived from the present work include as special cases those obtained by Thorpe for progressive internal waves <Thorpe, 1968a> and standing internal waves <Thorpe, 1968b>. Moreover, the solutions reduce to those derived for random surface waves by Sharma and Dean <1979> when the density of the upper fluid is taken as zero.