This paper criticizes the attempt to found the epistemological doctrine that all theories are evidentially underdetermined on the thesis that all theories have empirically equivalent rivals. The criticisms focus on the role of auxiliary hypotheses in prediction. It is argued, in particular, that if auxiliaries are underdetermined, then the thesis of empirical equivalence is undecidable. The inference from empirical equivalence to the underdetermination of total theories would seem to survive the criticisms, because total theories do not require auxiliaries to yield (...) observational consequences. It is shown that, nevertheless, underdetermination cannot be established for total theories. (shrink)