Fibromyalgia is a relatively common disorder, which occurs predominantly in women, that is characterized by widespread aching and stiffness in muscles. Although there have been numerous studies of fibromyalgia, its etiology has remained unclear, but it is generally believed that central pain processing abnormalities are involved. Neurotropin, a non-protein extract of inflamed cutaneous tissue from rabbits inoculated with vaccinia virus, has been used extensively in Japan for many years to treat a variety of chronic painful conditions, including fibromyalgia. This present protocol is a double blind, placebo-controlled, crossover study designed to examine the clinical efficacy of Neurotropin in treating women (neither pregnant nor lactating) suffering from fibromyalgia without evidence of any other cause of their complaint of pain. Patients must meet the American College of Rheumatology (ACR) diagnostic criteria for fibromyalgia and must agree to maintain a stable therapeutic regimen throughout the 25-week study.