Two expressions including the variance and the correlation coefficient between the level-crossing interval lengths of a stationary random process are derived. If the random process is Gaussian, one can estimate to some extent the correlation between level-crossing intervals. For the Gaussian process having low-pass or band-pass spectra of the seventh-order Butterworth type, the variance and the correlation coefficient are experimentally determined. The level-crossing intervals are found to be mutually dependent in most cases except low-pass spectrum.