A description of factors influencing perceptions of nonpharmacological treatment was derived inductively from interviews with people receiving chiropractic treatment for back pain, using grounded theory analysis. A theoretical model linking these factors was constructed, and was tested using interview data from a longitudinal study of people undertaking exercise therapy for dizziness. The model highlights the potential for reciprocal interactions between abstract beliefs relevant to illness and treatment and concrete experiences of therapy, and for interactions between perceptions of symptom change and of therapist competence. Therapist communication may modify abstract illness/treatment models and symptom perceptions, thus mediating effects of concordance on adherence and placebo effects.