This article is about the exchanges between Leibniz, Arnauld, Bayle and Lamy on the subject of pain. If commentators have extensively studied the Leibnizian solution to the mind-body problem, they have usually overlooked a recurrent objection that Leibniz’s Cartesian readers addressed to his hypothesis of a pre-established harmony: the problem of pain, or, more exactly, the capacity of the Leibnizian solution to account for the phenomenon of pain. In this article, I examine how this phenomenon is interpreted in Leibniz’s exchanges with Arnauld, Bayle, Lamy and Malebranche, who called attention to three difficulties raised by Leibniz’s approach to pain: the problem of concomitance between pain and bodily injury; the spontaneity of the soul which is hardly compatible with the unpleasantness of pain; and the difficulty in admitting that pain might be a natural representation of a physical state. In successively analysing these three objections, my purpose is twofold. First, I want to show that for Leibniz’s contemporaries, the mind-body problem could not be reduced simply to the issue of causation with which his commentators widely dealt. Second, I want to clarify Leibniz’s pre-established harmony by opposing a representational to a functional account of psychophysical phenomena. This opposition will allow me to indicate what was left unexplained by Leibniz’s seductive version of parallelism. A first version of this work has been presented in a seminar (2014/09/16) organized by Julie Klein at Vilanova University (Philadelphia, US).