In this paper, I enquire whether there are Kuhnian paradigms in medicine, by way of analysing a case study from the history of medicine—the discovery of the germ theory of disease in the nineteenth century. I investigate the Kuhnian aspects of this event by comparing the work of the famous school of microbiology founded by Robert Koch with a rival school, powerful in the nineteenth century, but now almost forgotten, founded by Carl Nageli. Through my case study, I show that (...) medical science possesses some Kuhnian features. Within each school, scientists used similar exemplars and shared the same assumptions. Moreover, their research was resistant to novelty, and the results of one party were disregarded by the other. In other words, in a moderate sense, the Koch and Nageli groups worked within distinct paradigms. However, I reject the stronger Kuhnian claim that the terms used within the two paradigms were mutually unintelligible. Focusing on the semantic aspects, I argue that no account of incommensurability of reference can be given in this case, although, for sociological reasons, the two parties talked past each other. I suggest in addition that the rival scientists could have understood each other more easily if their theoretical commitments had not been so deeply ingrained, and I use the example of Pasteur to indicate that the causal account of meaning might have avoided the communication breakdown. (shrink)