Evidence is presented that in adult human axillae there exists a third type of sweat gland tentatively designated as the apoeccrine sweat gland. This type of gland shows a segmental or diffuse apocrinelike dilatation of its secretory tubule but has a long and thin duct which does not open into a hair follicle. The electron microscopy of its dilated segment is often indistinguishable from that of the classical apocrine gland. The less remarkably dilated segment of the apoeccrine gland tends to retain intercellular canaliculi and/or dark cells. These apoeccrine glands are consistently present in adult human axillae regardless of sex or race. In the axillae of the two 6-yr-old subjects, both classical apocrine and eccrine glands were present but no apoeccrine glands were found. Between 8-14 yr of age, the number of large eccrine glands with or without partial segmental dilatation gradually increased. At 16-18 yr of age, the number of apoeccrine glands increased to as high as 45% of the total axillary glands. The data support the notion that apoeccrine glands develop during puberty in the axillae from eccrine or eccrinelike sweat glands.