We have assessed the DNA sequence requirements for the correct spatial pattern and phenotypic expression of y in the late embryo/larvae. The wild-type larval phenotype requires both the regions between -294 bp and -92 bp and a portion of the intron; the sequence element(s) located within the intron can act in a position independent manner to effect the wild-type larval phenotype. The larval expression pattern was examined by tissue experiments in situ and by staining germline transformants derived from various y/lacZ fusion constructs. The larval expression of y is restricted to the mouthparts, microsetae and anal plates. While the -495 bp to +194 bp region alone cannot effect a wild-type larval expression pattern, this region in conjunction with the intron appears to be sufficient to drive beta-gal expression in an essentially wild-type pattern. Our data further suggest that the -294 bp to -92 bp region contains elements which specify the larval pattern and that the element(s) in the intron normally act to enhance the level of expression necessary for the wild-type larval phenotype. We also present a phenotypic analysis of the adult cuticle structures of germline transformants derived from a variety of deletion and rearrangement constructs of the y gene. This analysis has revealed several new features associated with the regulation of y expression.