Electron microscopic investigation of scales of the goldfish Carassius auratus revealed that the lamellae of fibrillary plates contain sheet-like structures composed of vertically oriented collagen fibers embedded in an organic matrix. The fibers (TC fibers) are smaller in diameter (35-45 nm) than those of the lamellae and the matrix is stained intensely with lead citrate. The sheet-like structures as well as the lamellae are formed by fibroblasts located beneath the lamellae. The orientation of collagen fibers of the sheets and the lamellae seems to be controlled by the orientation of the ridges and invaginations of the surface of the fibroblasts. The fibrillary plate of C. auratus was found to be partially calcified. Calcification was initiated by the deposition of needle-like or flaky crystals of hydroxyapatite in the organic matrix of the sheet-like structure and proceeded into the TC fibers and the matric region of the lamellae. The potassium pyroantimonate-osmium tetroxide method showed a heavy concentration of calcium in the osteoblasts, fibroblasts, and in the matrix regions of the fibrillary plate. Calcium-containing precipitates were also present in the "hole zone" of the collagen fibers in the lamellae, but the significance of this location in calcification remains to be elucidated.