An algorithm for directly calculating third-order noise operation spectra, which includes no evaluation of the third-order correlation function as a preliminary stage, is found. For the Ershler-Randles circuit, an expression is found, which links bispectra of the equilibrium electrode potential fluctuation determined in the imaginary and real axes of the Laplace plane. Advantages of using the Laplace space in studies of the fine non-Gaussian structure of random time series are discussed.