Information on the complexity of mammalian RNA transcription has increased greatly in the past few years. Notably, thousands of sense transcripts (conventional protein-coding genes) have antisense transcript partners, most of which are noncoding. Interestingly, a number of antisense transcripts regulate the expression of their sense partners, either in a discordant (antisense knockdown results in sense-transcript elevation) or concordant (antisense knockdown results in concomitant sense-transcript reduction) manner. Two new pharmacological strategies based on the knockdown of antisense RNA transcripts by siRNA (or another RNA targeting principle) are proposed in this review. In the case of discordant regulation, knockdown of antisense transcript elevates the expression of the conventional (sense) gene, thereby conceivably mimicking agonist-activator action. In the case of concordant regulation, knockdown of antisense transcript, or concomitant knockdown of antisense and sense transcripts, results in an additive or even synergistic reduction of the conventional gene expression. Although both strategies have been demonstrated to be valid in cell culture, it remains to be seen whether they provide advantages in other contexts.