This clinical research study examined the music therapeutic process from sensorial play to musical form by psychotic patients. Based on the assumption that the psychic space has its origins in the transition from sensorial play to musical form, and that the capacity to make representations is severely affected by psychosis, there is a need to find out by which means this capacity can be re–established. Because of their pathology, they do not make use of a psychic space to reach symbolisation, which means in music–therapeutic terms that they are not able to create a musical form in which they could exist as a subject. Therefore the therapeutic transition from sensorial impression to musical form (i.e. proto–symbolisation) is a basic condition for the treatment of psychotic patients. In this contribution the author examines and describes the process from sensorial play to musical form. The phenomena sensorial play, moments of synchronicity and musical form are defined and the different characteristics are summarised. The specificity of the phenomena of silence, timbre and inter–subjectivity, which were essential to the therapeutic process, is discussed. The therapeutic interventions that are of central importance for the clinical music therapist are examined. Finally, the usefulness of the study for the clinical music therapist is made clear.