By using monoclonal antibodies to type II collagen and immunohistochemical techniques, we studied the distribution of type II collagen in the developing guinea pig ear. Type II collagen appearance and disappearance corresponded to cartilage development and resorption. Type II collagen was identified in Meckel's and Reichert's cartilages, the cartilage plate of the auricle and external acoustic meatus, the ossicles, eustachian tube cartilage, and the otic capsule. Type II collagen also appeared with the development of structures in noncartilaginous parts including the tympanic membrane, tympanic annulus, basilar membrane, spiral limbus, spiral ligament, and osseous spiral lamina, Rosenthal's canal, the maculae of the utricle and saccule, and the semicircular canal membrane, crista ampullaris, and endolymphatic duct. Type II collagen is distributed widely in the ear after the early stages of development. Thus, type II collagen should be considered an important structural component of the ear.