The nature of acetylated Sudan Black B (aSBB) has been investigated, and it has been found, by thin layer chromatography, that each fraction of aSBB has an Rf which is the same as that of a similar fraction of Sudan Black B (SBB). However, aSBB has been found to have fewer fractions, 9–12 than SBB, 14–16. The two major fractions from aSBB and SBB were examined, and a great similarity was found between the absorption spectra of the respective fractions of aSBB and SBB. The major fraction of aSBB was investigated by mass spectroscopy and found to have a similar molecular weight to that expected of SBB. This demonstrates that aSBB is not in fact acetylated, and that the components of aSBB are chemically no different from the corresponding components of SBB.