We h ave demonstrated t h at polyamide nucleic a cids complementary to the transactivation response (TAR) element of HIV-1 LTR inhibit HIV-1 production when transfected in HIV-1 infected cells. We have further shown that anti-TAR PNA (PNATAR) conjugated with cell-penetrating peptide (CPP) is rapidly taken up by cells and exhibits strong antiviral and anti-HIV-1 virucidal activities. Here, we pharmacokinetically analyzed 125I-labeled PNATAR conjugated with two CPPs: a 16-mer penetratin derived from antennapedia and a 13-mer Tat peptide derived from HIV-1 Tat. We administered the 125I-labeled PNATAR-CPP conjugates to male Balb/C mice through intraperitoneal or gavage routes. The naked 125I-labeled PNATAR was used as a control. Following a single administration of the labeled compounds, their distribution and retention in various organs were monitored at various time points. Regardless of the administration route, a significant accumulation of each PNATAR-CPP conjugate was found in different mouse organs and tissues. The clearance profile of the accumulated radioactivity from different organs displayed a biphasic exponential pathway whereby part of the radioactivity cleared rapidly, but a significant portion of it was slowly released over a prolonged period. The kinetics of clearance of individual PNATAR-CPP conjugates slightly varied in different organs, while the overall biphasic clearance pattern remained unaltered regardless of the administration route. Surprisingly, unconjugated naked PNATAR displayed a similar distribution and clearance profile in most organs studied although extent of its uptake was lower than the PNATAR-CPP conjugates.