Although Phenylbutyrate has been extensively used to treat patients with rare metabolic diseases, Phenylbutyrate is an investigational drug for the purpose of this study. Genistein is a naturally occurring substance that is found in food products such as soy and tofu, but is also an investigational drug for this study. When used together, both drugs may be able to restore normal chloride and salt (water) movements in body organs and glands in people with CF.