The complete amino acid sequence has been determined for two proteins, LmACP21 and LmACP22, which are prominent components of adult pharate cuticle from the migratory locust, Locusta migratoria. The proteins have relative molecular masses (Mr) of 16853 and 16879, respectively. They were purified by standard chromatographic methods, and the primary structures were determined by combined use of mass spectrometry and automatic Edman degradation. The proteins are characterized by the presence of a conserved, hydrophilic central sequence with pronounced similarity to sequences reported for cuticular proteins from other insect species, while the N- and C-terminal regions are dominated by the amino acids alanine, valine and proline. The electrophoretic identity of the two proteins was confirmed by matrix assisted laser desorption ionization mass spectrometry (MALDIMS) of the electroeluted LmACP21/22 proteins from a two-dimensional electrophoresis gel. The mass spectrometric analysis established the presence of additional proteins in close proximity to the LmACP21/22 gel spot. One of these proteins, Mr 16134, was identified as LmACP18, and enzymatic digestion indicated that it is structurally closely related to LmACP21 and LmACP22.