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The work presented in this thesis has two main themes. Firstly, it follows the development and initial evaluation of a new, hybrid FES orthosis for paraplegics. Secondly, it describes investigations which were intended to optimize the stimulus parameters used with the orthosis. One of the major limitations with pure FES standing and walking systems is rapid muscle fatigue. During quiet stance, chronic stimulation of support muscles is required which induces fatigue and significantly reduces their useful contraction time. Mechanical bracing provides safety, strength and protection of delicate joints but it lacks some of the features of FES. The "hybrid" orthosis, considered in this thesis, combines these two techniques so that the disadvantages of either technique alone are reduced. In the following chapters, the development of the mechanical braces, the sensors, the electrical stimulator and the controlling software are considered. Several preliminary investigations are reported which demonstrate the feasibility of the orthosis with regard to fatigue reduction and stability. In addition, tests are described which were designed to improve the characteristics of muscle and reflex activity for use with the system. The results of these tests showed that muscle dynamics could be improved by the addition of a single pulse to a regular stimulus pattern. Improvements were also obtained in reflex activity but to a less significant degree.