We assessed the effects of varying the treatment integrity of a prompting procedure on appropriate toy manipulation in two preschool-aged children with autism. Following an assessment to identify toys with high levels of inappropriate toy manipulation, each of three toys was associated with implementation of the prompting procedure at a different integrity level (10%, 50%, or 100%). For one participant, only the 100% integrity condition produced increases in appropriate toy manipulation. For the second participant, both the 50% and 100% integrity conditions produced increases in appropriate toy manipulation. These results suggest that integrity errors negatively impacted the acquisition of appropriate toy manipulation in children with autism, although the necessary level of treatment integrity varied across participants. (Contains 4 figures and 2 tables.)