Observations on successive sound and silence durations in spontaneous speech have revealed a regular structure. Periods of relatively long pauses coupled to short vocalizations were found to alternate with periods in which short pauses and long vocalizations were paired. It is shown that such a structure can be produced by a random selection of sound-silence durations from exponential distribution functions. A test for the statistical significance of this effect is proposed. © 1968, Sage Publications. All rights reserved.