I report that single-stranded antisense as a part of large circular (LC-) genomic DNA of recombinant M13 phage exhibits enhanced stability, sequence specific antisense activity, and no need for target site search. A cDNA fragment (708 bp) of rat TNF-$alpha$ was inserted into a phagemid vector, and TNF-$alpha$ antisense molecules (TNF$alpha$-LCAS) were produced as single-stranded circular DNA. When introduced into a rat monocyte/macrophage cell line, WRT7/P2, TNF$alpha$-LCAS was able to ablate LPS-induced TNF-$alpha$ mRNA to completion. The antisense effect of TNF$alpha$-LCAS was shown to be sequence-specific because expressions of three control genes ($eta$-actin, GAPDH and IL-1$eta$) were not significantly altered by the antisense treatment. Further, TNF$alpha$-LCAS was found to be highly efficacious as only 0.1 $mu$g (0.24 nM) of TNF$alpha$-LCAS was sufficient to block TNF-$alpha$ expression in 1$ imes10^5$ WRT7/P2 cells. I have also observed specific antisense activity in reduction of NF-$kappa$B gene expression. The results suggest that an antisense sequence as a part of single-stranded circular genomic DNA has a specific antisense activity.