In connection with the biogenesis of peptide-type ergot alkaloids, the authors have examined in detail if any cyclic dipeptide occurrs in ergot fungi. As a result, it has been found that, of all others, the ergot fungus capable of producing peptide-type alkaloids produces prolyldiketopiperazines corresponding to peptide portions of the peptide-type alkaloids. So far, the authors have isolated four compounds, L-leucyl-D-proline-lactam, a hitherto unknown prolyldiketopiperazine “B”, L-phenylalanyl-L-proline-lactam and L-phenylalanyl-D-proline-lactam, the former two from the sclerotia and saprophytic cultures of Elymus-type ergot fungus producing ergokryptine, ergosine and unknown peptide-type alkaloids, “P1” (4, 5) (ergohexine(6)) and “P2”(4, 5) (ergoheptine(6)), and the latter two from the sclerotia of the Hungarian Secale-type fungus containing mainly ergotamine. As was expected, the state of increase and decrease of prolyldiketopiperazines and peptide-type alkaloids in the culturing process suggested that the former would be the precursor of the latter. © 1970, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.