As more and more Pentecostal theologians are pursuing formal training in academic theology and philosophy, they are becoming increasingly sensitive to the importance of being conscious of one's theological method in systematic theology. This article is a suggestion that Pentecostal theologians would benefit from adopting as one guideline for their theological method a form of lex orandi, lex credendi called `the rule of spirituality and the rule of doctrine', which involves a reciprocal relationship between Pentecostal spirituality and doctrine. The goal of the relationship is doctrinal theology that is informed by legitimate aspects of Pentecostal spirituality and that is able to correct illegitimate aspects of it. After the method is established, three aspects of Pentecostal spirituality are chosen to inform a Pentecostal doctrine of the Lord's Supper. Finally, aspects of this doctrine of the Supper are employed to critique other aspects of Pentecostal spirituality.