The Picture Exchange Communication System (PECS) is an intervention programme designed for use with children with autism or other severe communication deficits. Three children (two with autism and one with Down syndrome) with very limited functional communication skills were trained to use PECS, using a multiple baseline design across participants. The children were observed throughout their baseline and intervention periods and communicative forms and success of their initiations of c.ommunication were recorded. Generalisation of the training into the natural classroom setting and into the childrens' homes was measured. Due to an increase in the childrens' use of PECS as a form of communication, the children were observed to increase their frequency and success of initiating communication in their classrooms. Two of the children began using PECS at home with full support from their parents/guardians, and as a result their frequency and success of initiating communication in the home also increased. The relationship between the introduction of PECS and changes in other dependent variables, namely increased speech and improved behaviour management, are considered. Implications of the research and suggestions for future investigations are also discussed.