Preferences of 2 children with developmental disabilities, whose functional analyses indicated that their problem behavior was maintained by access to tangible items, were assessed using three formats (i.e., paired stimulus [PS], multiple-stimulus without replacement [MSWO], and free operant [FO]). The experimenter administered each format five times and compared levels of problem behavior across formats in a multielement design. Both participants exhibited problem behavior in PS and MSWO formats but not in the FO format. Results are discussed in terms of recommendations for practitioners. (Contains 1 figure.)