The mass spectral fragmentation of the cyclodipeptides were investigated. The main fragmentation processes for the peptides were almost the same. In the case of compounds that have the large side chains, the cyclic skeletal ions generated by the loss of the side chain group were followed by the further fragmentations. The important ions arising from cycloglycylglycine in 70 eV-mass spectrum were of m/z 86 [M-CO] and of m/z 71 [M-NHCO] from which further fragmentations occurred. The metastable ion spectrum by B/E linked scan method indicated that the m/z 30 (the most abundant ion in 70 eV-mass spectrum) was formed from the process via the ion of m/z 86.
