The neighboring genes gstD1 and gstD21 share 70% sequence identity. gstD1 encodes a 1,1,1-trichloro-2,2-bis-(P-chlorophenyl)ethane dehydrochlorinase; gstD21, a ligandin. Both of their mRNAs are inducible by pentobarbital but otherwise behave very differently. Intact gstD21 mRNA is intrinsically labile, but becomes stabilized when separated from its native untranslated region (UTR). In contrast, whereas gstD1 mRNA is very stable in its entirety, without its native UTRs it becomes even more labile than that of gstD21. Decay patterns from four chimeric D1-D21 mRNAs, designed to reveal the individual importance of each molecular region to stability, strongly indicate the presence of destabilizing elements in the coding region of gstD1 mRNA. Thus, the UTRs of this molecule must contain a dominant stabilizer element that overrides the destabilizing influence of the coding region and confers overall stability to the entire molecule. The suspected presence of such a stabilizer element in gstD1 mRNA extends a concept from mRNA metabolism in yeast and cultured mammalian cells to include a multicellular organism, Drosophila melanogaster. The complementary presence of destabilizing and stabilizer elements on the same mRNA reveals a regulatory mechanism by which an abundant mRNA can be further induced by a chemical stimulus, or otherwise be returned to normal levels during recovery.