The association of positive patient expectations with placebo responses is well recognized. However, the potential role of health care providers' behavior in modeling these expectations has not been adequately established, The overall goal of this proposal is to describe and quantify placebo effects in a trial of acupuncture for osteoarthritis (OA) of the knee. No previous studies have scientifically evaluated the effects of communicative style in providers of alternative and complementary medicine, and tile placebo response that may result. This proposal will examine placebo responses in the context of practitioner-patient interactions at the time of the acupuncture treatment. The study will have three phases: Phase 1 will include a qualitative component to determine potential patient-related determinants of placebo response, such as beliefs and expectations towards treatment of knee OA with acupuncture, in phase 2 we will develop and test an instrument to measure evaluate outcome and self efficacy expectations. Phase 3 will be a nested RCT to evaluate practitioner-patient interactions and placebo responses. The experimental design will include two stages or randomization. Patients will initially be randomized to one of two different structures of practitioner-patient interaction. Acupuncture practitioners will be trained to behave following semi-structured communicative styles, including traditional approaches in Chinese Medicine, and techniques previously described in patient-doctor communication studies. Within each of these groups patients will be further randomized to receive acupuncture or sham acupuncture. In addition there will be a natural control group (waiting list group), in which patients will be offered acupuncture three months after study entry.