Distri-bution, macroscopic morphology and biological function of the so-called sternal gland is described in all genera of Platyrrhini except in Marikina and Chiropotes, from which no material was available. The gland can be found, varying slightly in different genera and species, on the ventral surface from the gular to the epigastric region. The gland is developed during ontogenesis and was first seen macroscopically in older fetuses of Hapalidae, reaching its full differentiation in dominant adult animals, especially in males. It can be observed to be functioning in animals aged less than 2 years. Many adults, low in social order, had externally or macroscopically almost no gland. Dried skins and fixed tissue, as well as living specimens were studied. In Hapalidae 4 features were observed in different combinations in the various genera, whereas larger glandular fields dominated in the Cebidae. The features existing in Hapalidae are: A hemispherical glandular area at the articulation of sternum and claviculae. A brush of hairs differing in diameter and coloration from the pelage and caudad of 1. A ribbon-like field of nearly naked glandular skin which extends caudad of 1 and 2 almost to the navel. In Aotes the same features occur in regard to arrangement, dimension and position. A rhombic area in the gular region is observed in Leontocebus rosalia only. The gland in the genera Pithecia, Alouatta and Brachyteles appears to be similar. Among Cebidae only an epigastric glandular area which was apparent in specimens of Cebus capu-cinus, Cebus griseus and Cebus apella, as well as Cacajao rubicundus. In Lagothrix the ventral surface of the trunk is covered with long, very dense hair, which differs markedly from the main pelage and makes the identification of the gland difficult in living animals. However, preserved material, secretion on the hair and marking behavior show the presence of the gland. The sternal gland of Ateles is known as "2 circular white areas of skin over the manubrium of the sternum, which are slightly elevated".