We examined the dynamics of removal from circulation, tissue distribution, and persistence of phosphorothioate oligodeoxynucleotides (S-ODN) anti-tumor-necrosis-factor and a control of random sequence (randomer) in mice. After intravenous injection, the majority (96%) of S-ODN cleared rapidly from the circulation in the first two phases. In the first phase, 37.8 +/- 2.3% of the radioactivity had a mean half-life (t1/2) of 2.0 +/- 0.4 minutes. In the second phase, 58.1 +/- 1.5% of the radioactivity cleared with t1/2 of 12.6 +/- 0.2 minutes. The catabolic phase, constituting a minor proportion (4.1 +/- 0.8% of the total radioactivity), had a mean t1/2 of 2.7 +/- 0.5 hours. At a low dose (1 microgram) tissue distribution of both S-ODN anti-tumor-necrosis-factor and randomer were similar. The liver and kidneys were the major organs involved in uptake and removal of S-ODN. Autoradiographic studies showed the liver Kupffer cells to be the major site of uptake and renal urinary space for elimination. The clearance rate from the circulation was increased with the dose of S-ODN. In contrast, the fraction of radioactivity localized in the kidneys, liver, and spleen was decreased with increase in dosage. Furthermore, at a high dose (200 micrograms), the tissue distribution of the S-ODN anti-tumor-necrosis-factor differed significantly from the randomer. These findings have general significance in showing that the liver and kidneys are the major organs for removal of S-ODN and these organs are saturable at high doses. In addition, the results have specific importance in defining different parameters, dose and base composition, that affect utilization of antisense oligonucleotides for controlling gene expression in vivo.