ABSTRACTWe implemented a series of time-lagged multiple probe designs using counterbalanced probes to determine the variables that control the emergence of stimulus equivalence (i.e., derived relations), among participants with autism and significant cognitive/language delays, who did not demonstrate derived relations during the preintervention measures. In Experiment 1, we trained a frame of symmetry using a computer-based cross-modal matching procedure, which required the participants to match auditory and visual stimuli. Three of the four participants demonstrated transitivity during the postintervention probe trials, using an unrelated set of stimuli to the training set. Participant 4, who did not acquire the derived relations indicative of stimulus equivalence, also lacked an echoic repertoire. In Experiment 2, we trained symmetry relations using multiple exemplar instruction (MEI) across visual stimuli. Following the MEI for visual symmetry relations, none of the participants demonstrated responses in accordance with stimulus equivalence. In Experiment 3, we investigated the role of the vocal tact operant in the acquisition of derived, stimulus equivalence relations, among the three participants from Experiment 2. During the postintervention probe trials with novel stimuli, all three participants demonstrated the derived relations indicative of stimulus equivalence. Collectively, the results suggested that, prior to the acquisition of emergent relations, one must demonstrate symmetry (bidirectional) relations, along with a vocal tact repertoire.