This thesis investigated the effects of adding the learning of American Sign Language (ASL) signs (as part of the Applied Behavior Analysis) on the negative behaviors of seven developmentally disabled children (aged 8-13 years). The children were measured on the following: overall disruptive behavior; aggressive behavior; tantrums; and the use of ASL signs over the course of 20 consecutive school days (10 days for the establishment of the baseline, 10 days for the study of the intervention). Results on these measures failed to provide support for the efficacy of ASL signs. Qualitative observations, however, did lend support for the use of the intervention. The lack of quantitative findings is explained by the fact that signs were being implemented before the baseline period and that most of the dramatic treatment gains had been obtained before the baseline measurements were completed. Although the study did not provide hard evidence for the efficacy of using ASL with the developmentally disabled population, there was enough anecdotal evidence to consider applying this intervention. The advantage of ASL is that even if it is not effective, the iatrogenic effects of using it are minimal at most. The findings from this study suggest that caretakers who take the time to implement ASL signs into the behavioral repertoire of developmentally disabled children will see dramatic improvements in the child's behavior. Two appendices containing behavior rating scales and 78 references are included. (KFT)