Preclinical and clinical data suggest that subcutaneous or intravenous administration of neurotrophic factors may be effective for the treatment of peripheral nervous system diseases. However, even though these proteins are natural products, they do present specific problems when used as therapeutic agents. They cannot be given by the oral route. They may elicit an immune response. Their pharmacokinetic behaviour is difficult to predict due to binding to other macromolecules and differential sensitivity to proteinases. Penetration into peripheral nerve sheets may be limited. Large scale production is labour and cost intensive. Small organic molecules as used in the “typical drugs” tend to be superior to protein therapeutics in most, if not all, of these aspects.