The structure and histochemistry of the palmar and plantar skin were studied in four adult male marmosets (two Callithrix jacchus and two Callithrix penicillata). In this skin there exist well-developed epidermal ridges, to which are attached one or two ducts of sweat glands. A thick stratum corneum can be seen in the epidermis, while a distinct stratum lucidum cannot be isolated from the other layers. The stratum granulosum is constituted by one or three layers of cells containing keratohyalin granules. Melanin granulations are mainly concentrated in the basal cells of the epidermal ridges. Dendritic melanocytes and amelanotic melanocytes containing alkaline phosphatase are found among the epidermal cells. Glycogen, UDPG-GT and phosphorylases are mainly present in the middle and lower Malpighian cells of the epidermal ridges. Alkaline phosphatase, ATPase, alanyl amino-peptidase and leucine aminopeptidase were absent in the epidermal cells. SDH, cytochrome oxidase, MAO and a certain number of NAD-dependent dehydrogenases (LDH, ADH, MDH, alpha-GPDH, beta-OHBDH and GDH) showed a stronger reactivity in the basal cells and Malpighian layer. The NADP-dependent enzymes (G-6-PDH, 6-PGDH, cis-aconistase and ICDH) were more reactive in the upper Malpighian layer and stratum granulosum. The stratum corneum showed some acid phosphatase and nonspecific esterase reactivity. The collagenous fibers intertwined with a small number of very thin elastic ones and a larger amount of reticular fibers run almost parallel to the epidermal ridges in the papillary body. In the reticular dermis some fibers are disposed transversely to the epidermal ridges. Meissner corpuscles reactive to butyrylcholinesterase, acetylcholinesterase, nonspecific esterase and G-6-PA are disposed at regular intervals and frequently at each side of the epidermal ridges. Pacinian corpuscles were found only in the hypodermis. The eccrine sweat glands contain glycogen, UDPG-GT and phosphorylase in their secretory, ductal and myoepithelial cells. The secretory part shows a uniform reactivity for every dehydrogenase because it contains only one type of cells (clear cells). The intraepidermal segment of the ducts shows a stronger reactivity to nonspecific esterase and NADP-dependent dehydrogenases than the epithelial cells around it.