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Due to the presence of gross magnetic susceptibility artifacts, functional MRI (fMRI) has proved problematic in studies of the human inferior frontal cortex (IFC). There is a strong desire, therefore, to employ techniques that mitigate susceptibility artifacts in the IFC while preserving the imaging parameters of an fMRI study. It has been shown that the use of a single, strongly diamagnetic, intra-oral passive shim significantly improves the homogeneity of the static magnetic field (B0) and, as a result, alleviates the susceptibility artifacts within the IFC. In this study, practical issues regarding the use of an intra-oral passive shim are examined. We investigated B0 instabilities within the IFC resulting from subject head motion in order to calculate the effects of an intra-oral passive shim on the temporal variance of an EPI time series. These studies show that the addition of an intra-oral passive shim improves both B0 homogeneity and signal stability, and increases sensitivity to functional activation. Magn Reson Med 50:1089–1094, 2003. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]