Among the least studied of the works of Theodore of Mopsuestia is his Dispute with the Macedonians, a text that purports to be a transcript of an actual debate held in the city of Anazarbus sometime in the last decade of the fourth century. Although it has been justly said that the treatise is “surely not his most significant writing,” it does offer a rare opportunity for comparative analysis since Theodore’s catechetical homilies on the creed are also preserved, the final two of which are devoted to pneumatology. Therefore, this paper will proceed as an analysis of the teaching on the Spirit contained in the two works in order to set them in a more precise relationship one to another. While a comparison of the two texts shows that certain notions are common to both, it also is evident that in his engagement with the Macedonians Theodore was forced to deal much more extensively with the question of the Spirit’s procession, a topic that he barely touched upon in the catechetical homilies. In his treatment of this issue he drew upon and further developed arguments already put forward by Gregory of Nazianzus, but notably does not draw upon the tradition of Alexandrian pneumatology represented by Athanasius, Didymus, and later Cyril, which emphasized the Spirit’s relation to the Son. This paper therefore sheds light on a little known episode in the debates over the Spirit that took place in the late fourth century, and highlights Theodore’s distinct contribution to them.