The young Xenopus tadpole is a relatively simple vertebrate in which to explore the fundamental organisation of neuronal systems controlling motor behaviour. Immediately after hatching, these animals show distinct responses to particular stimuli, ranging from simple reflex bends or sustained rhythmic swimming when touched, to strong rhythmic struggling movements when grasped. Synaptic inhibition plays a key role in controlling all these responses. A small population of GABAergic reticulospinal neurons, which reliably terminate episodes of swimming when excited to fire by trigeminal afferents innervating the head skin, has now been characterised. These neurons may also play a role in control of long-term responsiveness to sensory stimulation. During self-sustained swimming, glycinergic inhibition from spinal interneurons has several distinct effects. Swimming frequency is very sensitive to changes in glycinergic inhibition. In contrast, rhythm generation and the left-right co-ordination mediated by characterised reciprocal inhibitory interneurons remain robust even after extensive surgical and pharmacological interference to inhibitory connections. These results have highlighted shortcomings with the use of the competitive antagonist strychnine in exploring the role of glycinergic inhibition. The spinal interneurons that control the gating of sensory transmission from trunk skin Rohon-Beard neurons during swimming have also been characterised. In addition to their role in swimming, these interneurons are strongly recruited during the struggling motor pattern, which, unlike swimming, is readily disrupted by glycinergic block.