The aims of the present study were to analyze how l-Dopa allows parkinsonian patients to increase their gait velocity and to compare these l-Dopa-induced modifications with those achieved by consciously attempting to walk as fast as possible (intentional modulations). The ‘intentional modulations’ of velocity were also compared with those of healthy elderly subjects. The results showed that parkinsonian patients walked more slowly, with shorter strides and shorter durations of swing phase, and longer durations of stance and double support phases, although no differences were observed for cycle duration. The mechanisms involved in increasing gait velocity were found to differ according to whether this was achieved through the action of l-Dopa, or by intentional increases in velocity. Intentional increases in velocity were greater than those caused by the effect of l-Dopa. The patients, however, used efficient strategies to increase their velocity when under the influence of l-Dopa. As l-Dopa leads to a ceiling effect on stride length, the patients can increase their velocity by modifying the cycle to such an extent that it compensates for the limitation in stride length. This strategy effectively increases velocity, despite the l-Dopa ceiling effect. The effects of l-Dopa on locomotion and, more generally, on motor control aspects are discussed.