Previous studies have demonstrated the presence of the calcium-binding proteins parvalbumin (PARV) and calbindin D-28k (CALB) in interdigitating neuronal systems of the primary visual cortex of primates (Celio et al. 1986; Hendry et al. 1989; Van Brederode et al. 1990). Since the processing of visual information takes place in the higher cortical areas (Hubel 1982), we wondered if complementarity of expression is maintained in the secondary visual cortex (area 18). We therefore examined tangential and coronal sections from the occipital lobe of squirrel monkeys using immunohistochemical techniques employing polyclonal antibodies against PARV and CALB. The pattern of PARV immunoreactivity is characterized by tangentially organized, alternating thick and thin stripes, separated by areas of lower immunoreactivity. Both the thick and thin stripes consist of PARV-immunoreactive neuropil. CALB immunoreactivity forms mainly thick stripes containing large numbers of labelled neurons. Thus in area 18, these zones of increased immunoreactivity coincide with the compartments revealing increased cytochrome oxidase activity, whereas the distribution of PARV and CALB is almost complementary in the subcortical visual centre and in the primary visual cortex (area 17) of New World monkeys.