The absolute configuration of ergometrinine, C(19)H(23)N(3)O(2) {systematic name: (6aR,9S)-N-[(S)-1-hy-droxy-propan-2-yl]-7-methyl-4,6,6a,7,8,9-hexa-hydro-indolo[4,3-fg]quinoline-9-carb-ox-amide}, was established based on epimerization reaction of ergometrine, which was followed by preparative HPLC. The non-aromatic ring (ring C of the ergoline skeleton) directly fused to the aromatic rings is nearly planar [maximum deviation = 0.271 (3) Å] and shows an envelope conformation, whereas ring D, involved in an intra-molecular N-H⋯N hydrogen bond, exibits a slightly distorted chair conformation. The structure displays undulating layers in the ac plane formed by O-H⋯O and N-H⋯O hydrogen bonds.