The purpose of exchange and development therapies (EDT) is to reduce the behavioural problems which are the expression of psychophysiological dysfunction. The aim of this study was to reveal the most disturbed psychophysiological functions and their evolution during the course of EDT in 42 children divided into three groups; group I--15 children with pure autism (A); group II--16 children with autism associated with neurological disorders (AA); and group III--11 children with pervasive developmental disorders (PDD). Among the 12 functions analysed, groups AA, A and APDD had respectively 8, 6 and 4 functions in which the score was high (> 2.5), indicating serious disorders (maximum 4). All the dysfunctions improved during EDT. However, each group had certain areas which were more susceptible to treatment. Further analysis of behaviour problems led to a more precise definition of the objectives and to the adaptation of the therapeutic methods to obtain greater effectiveness.