In this paper I discuss the dialogues between 'Protagoras', Theodorus and Socrates in "Theaetetus" 161-171 and emphasise the importance for this passage of a dilemma which refutation is shown to pose for relativism at 161e-162a. I argue that the two speeches delivered on Protagoras' behalf contain material that is deeply Socratic and suggest that this feature of the speeches should be interpreted as part of Plato's philosophical case against relativism, reflecting the relativist's own inability to defend his theory from attempts (...) to refute it. I then discuss Theodorus' role in the refutation of Protagoras and argue that his voice is needed to get relativism disproved in the self-refutation argument of 171a-c. I conclude with a brief discussion of the image of Protagoras at 171d. (shrink)