Proteins were extracted from the cuticle of mid-instar nymphs of locusts, Locusta migratoria, and cockroaches, Blaberus craniifer. Seven proteins were purified from the locust extract and five from the cockroach extract, and their amino acid sequences were determined. Polyacrylamide gel electrophoresis indicates that the proteins are present only in the post-ecdysially deposited layer of the nymphal cuticles. One of the locust and one of the cockroach nymphal proteins contain a 68-residue motif, the RR-2 sequence, which has been reported for several proteins from the solid cuticles of other insect species. Two of the cockroach proteins contain a 75-residue motif, which is also present in a protein from the larval/pupal cuticle of a beetle, Tenebrio molitor, and in proteins from the exoskeletons of a lobster, Homarus americanus, and a spider, Araneus diadematus. The motif contains a variant of the Rebers-Riddiford consensus sequence, and is called the RR-3 motif. One of the locust and three of the cockroach post-ecdysial proteins contain one or more copies of an 18-residue motif, previously reported in a protein from Bombyx mori pupal cuticle. The nymphal post-ecdysial proteins from both species have features in common with pre-ecdysial proteins (pharate proteins) in cuticles destined to be sclerotised; they show little similarity to the post-ecdysial cuticular proteins from adult locusts or to proteins from soft, pliable cuticles. Possible roles for post-ecdysial cuticular proteins are discussed in relation to the reported structures.