Immunocytochemistry was used to demonstrate type II collagen distribution during normal development of the mouse inner ear and in two malformed inner ears. Patterns of inner ear abnormalities and type II collagen distribution were compared between the malformed labyrinth of a mouse mutation (disproportionate micromelia, Dmm) and otic explants exposed to the teratogenic action of an L-proline analog, L-azetidine-2-carboxylic acid (LACA). The results suggest that type II collagen is an important constituent of the developing inner ear's extracellular matrix. Disruptions of the spatial and temporal pattern of collagen type II can adversely affect morphogenesis of the inner ear. A common mechanism of action is postulated for the causation of both the genetic and teratogen-induced inner ear malformations (i.e. disruption of the secretion of collagens to the otic extracellular matrix).