Known determinations of the absolute configuration of guaianolides were collected and found to be few. The absolute configurations of guaianolides rest on the assumption that 7-H always has α-orientation. For matricin, only the relative configuration was determined. On the basis of a detailed study of the NMR spectra of matricin and its epimers, and of synthetic, NMR, and CD studies with its decomposition product, chamazulene carboxylic acid, we were able to reconfirm the accepted 3S,3aR,4S,9R,9aS,9bS configuration of matricin. Chirality 13:337–341, 2001. © 2001 Wiley-Liss, Inc.