In order to map the anatomical structures participating in the analysis and processing of visual information related to discrimination of form and colour, we measured with positron emission tomography (PET) regional cerebral blood flow (rCBF) as an indicator of metabolic activity in ten right-handed volunteers during visual discrimination tasks, namely reference, form and colour tasks. Form discrimination specifically increased rCBF bilaterally in the inferior temporal and cingulate gyri, and in the left superior temporal, left occipital lateral, and left angular gyri, whereas colour discrimination did so in the left occipital superior and lateral, left parahippocampal, left occipito-temporal medial (lingual), and left superior parietal gyri, and the right precuneus.