To face the aspects connected with VR environments' usability for psychotherapeutic applications means to dare a double challenge from a methodological point of view: from one side, the need to adapt and to integrate on a heuristic basis classic usability evaluation methods to specific artefacts such as 3D Virtual Environments for clinical applications; from the other hand, the problems arisen by integration of expert evaluation of VR environments user-based tests carried out in real context of use. The theoretical background of our analytical stance is based upon an ethnometodological approach, a perspective that gives evidence of how people, in specific social situations, are able to solve complex tasks producing shared meanings and achieving their goals during interaction. According to this perspective, the methodological objective consisted also in the identification of the usability requirements of the specific community of practice. The virtual environments considered were two of the four VR modules in the framework of the VEPSY project: Panic Disorders – Agoraphobia and Eating Disorders.