All pallidal neurones are believed to share the same chemical and morphological phenotype in primates. At variance with this idea is the present finding that calretinin (CR), a calcium binding protein, occurs only in a subset of pallidal neurones in squirrel monkeys. This chemospecific subpopulation comprises both large and small bipolar and multipolar neurones distributed according to a rostrocaudal decreasing gradient. The large neurones outnumber small neurones throughout the pallidum; they abound principally in the external pallidal segment, whereas the small neurones prevail in the internal segment. Some pallidal CR-positive neurones display dorsoventrally elongated dendrites, while others show dendrites radiating in all directions. These findings reveal that pallidal neurones form a chemically and morphologically heterogeneous population in primates.