Inclusion Criteria:

• Male and female subjects with incomplete (traumatic), chronic (defined as 18 months or more post spinal cord injury) SCI aged 18 to 65 years
• CSCI must be categorized in classes C or D in the ASIA impairment scale. (C = Incomplete impairment with motor function preserved below the neurological level, and more than half of key muscles below the neurological level have a muscle grade less than 3. D = Incomplete impairment with motor function preserved below the neurological level, and at least half of key muscles below the neurological level have a muscle grade more than or equal to 3).
• The level of the SCI must be between C4 and T10 (neurological)
• Subject has a measurable range of motion at the hips, knees and ankles and possesses potential propulsive activity (i.e. no functional contractures)
• Female subjects of childbearing potential (those who are not surgically sterile or who are less than 2 years postmenopausal) must be using two forms of birth control, including a primary and a secondary form and have a negative pregnancy test immediately prior to treatment. Primary forms of contraception include: tubal ligation, partner's vasectomy, intrauterine devices, birth control pills, and topical/injectable/implantable/insertable hormonal birth control products. Secondary forms of contraception include diaphragms, latex condoms and cervical caps; each must be used with a spermicide.

Exclusion Criteria:

• Any clinical evidence of recent fracture(s) within the last six months prior to study start.
• Any history of Multiple Sclerosis or peripheral demyelinating disease or neuromuscular disorder.
• Heart rate of less than 38 or greater than 100
• Ashworth spasticity score of 0/4 or 4/4 at the hip or knee.
• Subject whose medical condition requires mechanical ventilation.
• Lower motor neuron injury, such as those with conus medullaris or cauda equina injuries.
• Subject with lower extremity amputation or proximal femorectomy.
• Subject with pressure ulcers stages 3 and 4.
• Subject medically or mentally unstable in judgment of Investigator.
• Subject on tricyclic antidepressants such as nortriptyline, amitriptyline and imipramine.
• Subject with ASIA motor score of greater than or equal to 92.
• Subject with ASIA sensory score of greater than or equal to 200.
• Subject with history of seizure within 2 years prior to study start.
• Subjects who have participated in a clinical trial involving investigational medication within 30 days prior to administration of HP184 or placebo.
• Female subjects with positive urine pregnancy test.
• Female subjects who are breast feeding.