1. The content of cyclic AMP and cyclic GMP in ovaries of the silkworm, Bombyx mori, changed differently depending on development. 2. The extirpation of suboesophageal ganglion caused cyclic AMP to decrease and cyclic GMP to increase at different developmental stages. 3. The reversed changes in the cyclic nucleotides were brought about by implantation of the ganglion or by injection of the diapause hormone preparation. 4. No change in both cyclic nucleotides was induced in ovaries during the first 24 hr after an injection of the hormone, but the clear effects appeared after a lag phase of a few days.