Though often observed that the Acts narrative is the defining paradigm for Pentecostal doctrine and practice, in point of fact Mk 16.9-20 functions as the 'litmus test' of the early Pentecostal Movement's fulfilling of the apos tolic mandates given by Jesus and carried out by the church. Despite the well-known text-critical problems surrounding the passage, the place of Mk 16.9-20 was unrivaled within the early Pentecostal literature in position and significance. Drawing on methodological approaches including textual criticism, literary analysis, canonical criticism and Wirkungsgeschichte, this study argues for the reappropriation of Mk 16.9-20 in Pentecostal theology and practice. The study begins by identifying the place of Mk 16.9-20 in early Pentecostal literature, surveys early Pentecostal responses to the textual problems, and compares these responses with others of the period. This is followed by a re-examination of Mk 16.9-20 in the manuscript tradition, a modest attempt to identify the origin of these non-Markan verses, and a discussion of their authority. The final major section of this article offers a variety of literary, theological and canonical observations on this 'Longer Ending'. The study concludes with an invitation to those within the Pentecostal tradition to reappropriate this most significant passage in the articulation of contemporary Pentecostal theologies.