Magnetic resonance imaging of changes in cerebral blood oxygenation (CBO) delineated areas of neural activation during self-paced unilateral middle finger tapping in five normal volunteers. Four contiguous imaging sections parallel to the bicommissural plane covered the hand area of the primary sensori-motor cortex bilaterally. All measurements were performed at 2.0 T using rapid gradient-echo sequences (TR/TE = 63/30 ms) with high spatial resolution (0.8 x 1.6 x 4 mm) and both strong (40 degrees flip angle) and weak (10 degrees) radiofrequency excitation pulses. This allows differentiation of flow and CBO contributions to the observed signal alterations. Functional cooperativity was analysed by a pixel-by-pixel correlation of signal intensity time courses with the stimulus protocol. Areas of activation included the contralateral primary motor cortex, the homologue part of the primary sensory cortex, the supplementary motor area (SMA) and the lateral premotor areas in all volunteers. Task-related activation of ipsilateral primary motor cortex above a threshold correlation coefficient of 0.5 was seen in two out of five volunteers (at 40 degrees) and one out of five (at 10 degrees) when performing the right-hand task. The present MRI findings readily demonstrate in single subjects that the SMA is involved in self-paced finger tapping. Only sparse activation in the ipsilateral primary motor cortex is consistent with the motor paradigm used.