The development of effective training programs for persons with profound mental retardation remains one of the greatest challenges for behavior analysts working in the field of developmental disabilities. One significant advancement for this population has been the reinforcer assessment procedure developed by Pace, Ivancic, Edwards, Iwata, and Page (1985), which involves repeatedly presenting a variety of stimuli to the client and then measuring approach behaviors to differentiate preferred from nonpreferred stimuli. One potential limitation of this procedure is that some clients consistently approach most or all of the stimuli on each presentation, making it difficult to differentiate among these stimuli. In this study, we used a concurrent operants paradigm to compare the Pace et al. (1985) procedure with a modified procedure wherein clients were presented with two stimuli simultaneously and were given access only to the first stimulus approached. The results revealed that this forced-choice stimulus preference assessment resulted in greater differentiation among stimuli and better predicted which stimuli would result in higher levels of responding when presented contingently in a concurrent operants paradigm.