Red yeast rice (angkak, red koji) obtained as cultures of Monascus purpureus on rice was extracted and analyzed by HPLC. In addition to the known red, orange, and yellow pigments and the mycotoxin citrinin, a new Monascus metabolite was detected. It is present in the original red yeast rice and formed in higher amounts when red yeast rice is heated. High-resolution mass spectrometry indicated the molecular formula C(15)H(12)O(4). The chemical structure was elucidated by analysis of NMR data. The new compound, named monascodilone, is characterized by a propenyl group on a pyrone ring, an aromatic ring, and a gamma-lactone group.