Existing literature on mineral springs in early modern France suggests that composition played a minor role in the evaluation of those springs. In fact it played a major role from at least the beginning of the seventeenth century. Composition was studied by a wide range of actors, from physicians in the provinces to chemists at the Paris Academy of Science, with a view to establishing the efficacy of particular springs against particular diseases. Iatrochemistry played a complex role in these evaluations. Followers of Paracelsus and van Helmont were among the first to perform chemical analyses on mineral waters. But there were physicians who studied composition without chemistry, or who used chemistry while opposing iatrochemistry. Conversely, there were iatrochemists who used chemistry to study mineral waters but not to evaluate them, and there were many chemists who gave at least as much weight to clinical experience as they did to composition.