Historians of physics have recently been taking a searching look at experimental practice. We should expect, however, that previously unexamined areas of science will yield previously unnoted aspects of the "dialogue between theory and experiment."² I contend in this paper that the events in superconductivity research after the second world war do just this. More specifically, I will try to show that the work of U.S. experimentalist Bernd T. Matthias confronts us with questions such as whether experimentalists always accept theoreticians' theories as useful; whether they share with theorists common criteria for what makes a theory useful or successful; whether, indeed, theoretical practice and experimental practice actually lead to disparate or competing theories.