THE nature of the aromatic component responsible for the tanning of the cuticle of blowfly puparia is not entirely clear. Pryor, Russell and Todd1 isolated protocatechuic acid from puparia of Calliphora erythrocephala, but could not find any phenolic material in Lucilia caesar. They used large quantities of insects preserved in sulphur dioxide solution. I have re-investigated the problem on small quantities of fresh material, using paper chromatograms.