Allatostatins are a family of insect neuropeptides that inhibit juvenile hormone biosynthesis by the corpora allata. We have characterized cDNA and genomic DNA sequences that specify a preproallatostatin precursor in the oviparous cockroach Periplaneta americana. Comparison of this precursor with that previously described [Donly, B. C., Ding, Q., Tobe, S. S. & Bendena, W. G. (1993) Proc. Natl Acad. Sci. USA 90, 8807-8811] for the viviparous cockroach Diploptera punctata revealed several common features. First, the precursors are remarkably similar in size and the organization of the peptides within the precursor is conserved. The separation of the peptides into groups by acidic domains within the precursor has been maintained. The P. americana precursor contains 14 allatostatin-like peptides that contain the core C-terminal sequence (Tyr/Phe)-Xaa-Phe-Gly-(Leu/Ile)-NH2, as compared to the D. punctata precursor, which contains 13. Five of the peptides are perfectly conserved between the two species. The remainder, with one exception, contain amino acid substitutions in the N-terminal address portion of the peptide. Several features of expression are also similar between these two species. In both, a single copy gene specifies a large allatostatin transcript of 5.0 kb in P. americana and 9.2 kb in D. punctata. In P. americana, allatostatin transcripts appear to be produced by numerous cells in different regions of the brain.