The neuronal mechanisms underlying initiation of motor responses in mammals are still poorly understood. We are exploring these processes in a simpler model system, the Xenopus tadpole. The neurons and connections providing a simple cutaneous crossed flexion reflex have been described (Li et al. 2003). However, the relationship between this reflex, an equivalent ipsilateral reflex (Li et al. 2004), and the mechanism for initiation of locomotion (swimming) is unclear. We have started to analyse the pattern of responses following brief, unilateral stimulation of a known cutaneous sensory pathway, from mechanosensory Rohon-Beard neurons. Ventral root recordings of motor responses were made in stage 37/38 Xenopus tadpoles immobilised in 10 μM α-bungarotoxin. A suction electrode was used to stimulate (single 0.5 ms stimuli) the sensory neurites of Rohon-Beard neurons in the tail skin on one side. Tadpoles were spinalised close to the hindbrain-spinal cord boundary (caudal to the 2nd post-otic myotome segment). For stimuli close to threshold for a response, around 76% of tadpoles (13/17) showed a short burst of motor discharge on the contralateral side at a latency in the range 8-15 ms. This would produce a reflex flexion of the body away from the stimulus. In a further four cases, a short latency reflex response was recorded only on the stimulated side. The short latency response was typically followed at a longer latency (25-50 ms from stimulus) by the start of swimming. Here discharge alternated between left and right sides at a frequency of 10-20 Hz. In most cases (10/17), the first swimming burst was on the stimulated side, irrespective of the side of the shorter latency reflex response; in fewer cases (3/17) it was on the opposite side. In the remainder the sidedness was unclear. Our recordings help define the events occurring shortly after a cutaneous stimulus and indicate that initiation of both reflex and swimming responses show distinct sidedness. At present, the mechanisms that determine this sidedness of response, and the relationship between the neuronal mechanism underlying reflex responses and the initiation of long-lasting swimming remain unclear.