The morphological changes of the neurosecretory cells of the brain of Bombyx mori after the experimentally severance of nervi corporis cardiaci were investigated with the electron microscope. In noumal brains, the neuosecretory cells in pars intercerebtralis of procerebrum were observed in detail and classfied into four cell types (type I, II, III and IV). After the severance of nervi corporis cardiaci, remarkable retrograde denaturation was seen in type I cells. The rER of type I cells changed to non-swollen forms and most of their neurosecretory granules decreased their electron densities. The type II and type III cells, however, showed no morphological changes. The neurosecretory granules in the axon processes were still electron dense and did not change their sized and numbers. These facts suggested that the axons of type I cells were broader in diameter than those of other cell types so that they were conspicuously denaturated bu the severance. The interaction between the denaturated neurons and the production of the neurosecretory materials were also discussed.