Recovery of useful motor function in humans with spinal cord injury (SCI) is a primary and elusive goal. In this preliminary study, we describe efforts to delineate the pharmacological effects of 4-aminopyridine (4-AP) on gait parameters in spinal cord injured humans who have retained some capacity to ambulate bipedally. A sequential entry, open label study was made of the effects of a single oral administration of an immediate-release formulation of 4-AP on the time-course profile of changes in component parameters of bipedal gait in ambulatory volunteers with chronic SCI. Nine healthy, rehabilitated, community-adapted male volunteers (six tetraparetic, three paraparetic), who sustained their injuries more than one year prior to entry into the study, ingested a single 10-mg dose of 4-aminopyridine after an overnight fast. Gait analysis parameters included velocity (meters/min), cadence (steps/min), stride length (meters), gait cycle (seconds), and double limb support (percent of gait cycle). They were measured for 24 hours using a sampling-rich strategy (nine duplicate measurements over 24 hrs). Repeated measures (randomized block) analysis of variance (ANOVA) and paired t-tests were used to test for the significance of differences between means and variances. The apparent pharmacological effect of 4-AP is associated with statistically significant changes in one or more of the component elements used to assess the characteristics and efficiency of bipedal gait. These changes in gait analysis parameters correspond temporally with the improvements in pulmonary function and heart rate variability previously described by us. 4-AP appears to enhance gait in a subset of humans with SCI. In this preliminary study we report, for the first time, an apparent effect of 4-AP on gait in spinal cord injured humans and suggest that the pharmacological effects of 4-AP may have clinically significant application in the restoration of useful motor function.