Stimulus-stimulus pairing (SSP) of vocalizations pairs the speech of others with the delivery of highly preferred items. The goal of this procedure is to produce a temporary increase in vocalizations, thus creating a larger variety of sounds that can subsequently be brought under appropriate stimulus control (Esch, Carr, & Grow, 2009). In this study, the authors evaluated the differential effects of 2 variations of a stimulus-stimulus pairing procedure on the vocalizations of 2 children with autism. For both participants, presenting 1 sound per pairing trial resulted in a higher rate of vocalizations than 3 sounds per pairing trial. (Contains 1 figure.);