BACKGROUND: Bonafide psychotherapy is an effective treatment for generalised anxiety disorder compared to no-treatment. Rather than creating increasing numbers of new overall treatment-packets within a medical meta-model, an additional approach to investigating clinical research designs may be to increase the understanding of already effective psychotherapies. Treatment manuals and protocols allow a relatively high degree of freedom for the way therapists implement the overall treatment manuals. There is a systematic lack of knowledge on how therapists should customise these overall protocols. The present study experimentally examines three ways of conducting a bonafide psychotherapy based on a 15 session time-limited cognitive-behavioural therapy (CBT) protocol and their relation to the therapists' protocol adherence and treatment efficacy. METHODS/DESIGN: This trial will investigate three different methods of customising a bonafide CBT-protocol using dyadic peer-tutoring methodology (primings). The individuals with GAD will be randomly assigned to one of three priming conditions (resource priming, supportive resource priming, or adherence priming). The participant treatment allocation will be performed randomly. Therapists will be assigned to a peer-tutoring partner and priming condition based on a mutual agreement. Treatment outcomes will be assessed at the following times: observer based in-session outcomes, session-by-session post-session outcomes, treatment outcome at post assessment and treatment outcome at 6-month follow-up. DISCUSSION: The proposed trial addresses the clinically relevant question of how to customise a bonafide psychotherapy protocol using tandem peer-tutoring methodology (three priming conditions). Through the development and testing of the proposed priming procedures, this study describes levels of adherence and how to conduct an overall treatment protocol in a more systematised way.