The expression profile of the monoclonal antibody SMI-32 was examined in the superior colliculus of adult marmosets. This antibody recognises subunits of the non- and dephosphorylated neurofilament protein, labelling predominantly neuronal perikarya and dendrites. The densest cellular label was observed in the intermediate layers (primarily, the stratum griseum intermediale), consisting of large multi- or bipolar neurones which were preferentially located within cytochrome oxidase-rich regions. The morphological characteristics of neurones showing heavy staining resemble those of extrinsic projection cells, suggesting a correlation between neurofilament content and axonal length.