Light and electron microscopy of a sural nerve biopsy obtained from a patient with giant axonal neuropathy revealed the presence of numerous axonal spheroids which were composed chiefly of neurofilaments. Large discrete masses of cytoplasmic microfilaments were also observed in endoneurial fibroblasts, endothelial cells, Schwann cells, perineurial cells and cultured skin fibroblasts. Neuronal degeneration in giant axonal neuropathy appears to be part of a generalized disorder of cytoplasmic microfilament formation.