A light and transmission electron microscopical study of 6 to 8 months old rabbit semilunar cartilages has shown that the cells in this tissue resemble chondrocytes more than fibroblasts. The prominent organelles in these cells were rough endoplasmic reticulum and the Golgi complex. An unusual finding was the occurrence of filamentous material in Golgi sacs and vesicles, and collagen fibrils within smooth membrane-bound tubular structures, apparently within the cells. Collagen fibrils forming fibres, fibre bundles and lamellae constituted the major component of the menisci. Protein-polysaccharide particles and associated fine filaments were found in the interfibrillary matrix and in the sparse territorial matrix adjacent to the chondrocytes. Numerous immature elastic fibrils, and rare mature elastic fibres with an electorn-lucent amorphous core, were also found in the general matrix amongst the collagen fibrils.