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The present study examined the effects of a mand training procedure on the rates of vocalizations in two infants. Both typically developing girls were less than six months old at the onset of the study. An ABCBC reversal design was employed to compare the rates of vocalizations in baseline conditions, a mand-training condition, and a differential reinforcement for other (DRO) condition. A state of deprivation was held constant for both infants across all three conditions in which neither infant was fed for one hour prior to the experimental session. The order of conditions was reversed for the second infant and sessions lasted no longer than three minutes one time per day. Findings suggested significant effects of the mand-training condition on increased rates of vocalizations for both infants. These results are discussed in terms of verbal behavior analysis, our assumptions about the developmental trajectory of the function of language, and the implications for early language intervention programs.