Experiments often disagree. How then can scientific knowledge be based on experimental evidence? In this paper I will examine four episodes from the history of recent physics: the suggestion of a Fifth Force, a modification of Newton’s law of gravitation; early attempts to detect gravitational radiation ; the claim that a 17-keV neutrino exists; and experiments on atomic-parity violation and on the scattering of polarized electrons and their relation to the Weinberg-Salam unified theory of electroweak interactions. In each of these (...) episodes discordant results were reported, and a consensus was later reached that one result—or set of results—was incorrect. I will examine the process of reaching that consensus. I will show that the decision was reached by reasoned discussion based on epistemological and methodological criteria. It then follows that we may use experimental evidence as the basis of scientific knowledge. (shrink)