This article demonstrates that Beckett’s play Not I derives from a hitherto unrecognised source: Rimbaud’s poem of synesthesia, ‘Voyelles’. Revealing the significant intertextual links between Beckett’s play and Rimbaud’s poem, I demonstrate that the striking central image of Not I – the disembodied mouth spewing out an almost incomprehensible torrent of words – directly recalls Rimbaud’s image for the vowel ‘I’ in ‘Voyelles’. Beckett uses Rimbaud, I argue, in a way that is distortive and translational: the image for ‘I’ is carried across languages and across sensory planes: from French to English, from words on the page to theatrical performance; from verbal to visual and sensory experience. The correspondences between Not I and ‘Voyelles’ are not only directly intertextual, however, but conceptual. Beckett draws particularly on two Rimbaudian concepts: the otherness of the poetic ‘I’, and the notion of a ‘dérèglement de tous les sens’. Adapting and translating Rimbaud’s conception of synesthesia in ‘Voyelles’, Beckett develops a theatrical mode that explores and manipulates various forms of cross-sensory experience, including synesthesia, to produce a ‘theatre of the nerves’.