Associated with Bayesianism is the claim that insofar as thereis anything like scientific theory-commitment, it is not a doxastic commitment to the truth of the theory or any proposition involving the theory, but is rather an essentiallypractical commitment to behaving in accordance with a theory. While there are a number of a priori reasons to think that this should be true, there is stronga posteriori reason to think that it is not in fact true of current scientific practice.After outlining a feature that distinguishes doxastic from practical commitment, I presentempirical evidence that suggests that, like perhaps all other theoretical commitment,scientific theory-commitment is doxastic.