 This study will assess the efficacy and the duration of efficacy of Botulinum toxin A Botox injected into the lumbar paraspinal muscles for reducing pain and disability in subjects suffering from chronic low back pain of six months duration or longer and arising from an identifiable muscle strain injury or back trauma. The treatment modality and techniques used are based on a successful prior 4 month open-labeled pilot study done by this research group, but will employ a prospective double-blind, randomized, cross-over design to control for any placebo or mechanical trigger-point injection effects. Subjects will also be assessed for a longer duration to better define the duration of efficacy. 