We report the isolation, full sequence characterization, amplification and expression properties of medfly chorion genes corresponding to the autosomal chorion locus of Drosophila. These genes are found adjacent to the paramyosin gene and are organized in the same order and tandem orientation as their Drosophila homologues, although they are spaced further apart. They show substantial sequence divergence from their Drosophila homologues, including novel peptide repeats and a new spacing of the tyrosines, which are known to be cross-linked in Dipteran chorion. The genes are amplified and expressed during oogenesis, as in Drosophila. Three of them are expressed in the same relative temporal order as in Drosophila but the fourth gene, the homologue of s15, shows a clear shift to an earlier expression period. This is the first known instance of changed temporal regulation in dipteran chorion genes.