The differentiation of cartilage in the external ear of the rat proceeds in four steps. Each of them is characterized by a specific biosynthetic activity of the chondroblast resulting in the appearance of a new structural component of the tissue: collagen fibrils, elastin fibers, cartilage ground substance and intracellular fat droplets. As a structurally and developmentally well-defined “subspecies” of cartilage, this tissue might serve as a suitable object for the experimental approach to some essential problems in histodifferentiation.