Though historians of religion have demonstrated that the theological commitments of early modern English people were labile and complex, there was nonetheless a prevailing sense in the period that belief posited bodily consequences. This article considers this bodily presence in John Donne’s poetry by exploring the humoral construction of religious identity in his Holy Sonnets. Donne’s conversion provided him with an unusual perspective: not many people were positioned to hold as nuanced a view of religious ideology. It is surprising, then, that when Donne considers his conversion — which he does in little and large in the Holy Sonnets — he casts it in somatic terms. Donne’s humoral constitution of faith in the Holy Sonnets anatomizes the vexed transactions of body and soul particular to late sixteenth- and early seventeenth-century thought. He depicts his body in the same terms that he uses to represent his religious temperament — as changeable and lacking integrity.