Prevertebral sympathetic ganglia develop markedly enlarged argyrophilic neurites as a function of age, gender and diabetes. Immunolocalization studies demonstrate their preferential labeling with antisera to highly phosphorylated 200 kDa neurofilament (NF-H) epitopes, NPY, peripherin and synapsin I, but not to hypophosphorylated NF-M and NF-H or MAP-2. The immunophenotype of dystrophic neurites in conjunction with the results of histochemical and ultrastructural studies are consistent with the terminal axonal and/or synaptic origin of neuritic dystrophy in the sympathetic ganglia of aged and diabetic human subjects.