A new peptide ergot alkaloid containing L-homoisoleucine, ergogaline, a new natural alkaloid of the ergotoxine family, has been isolated from ergot sclerotia of two strains of the field-growing parasitic fungus Claviceps purpurea grown on rye. This paper reports the isolation, identification and the crystal structure determination of ergogaline. The molecular and crystal structures have been studied by X-ray analysis [ergogaline monohydrate, monoclinic space group P2, with two molecules per unit cell of the dimensions a = 9.972(1), b = 10.902(1) and c = 14.761 (1) A, β = 94.05(1)°] and compared with the structures in solution as determined by 2D NMR spectroscopy.