Pertechnetate ion (TcO,) adsorption from aqueous solutions is compared between activated carbons derived from different sources, by reference to the distribution coefficient Kd of Tc between adsorbent and solution. Adsorption runs made in systems containing HCI and HN03, with pH parametrically varied by NaOH addition, proved Kd to rise with lowering pH in the acidic region in the case of activated carbon samples derived from coconut shell, from oil pitch, and from saw dust, but not in the case ofthose derived from coal or bone. In certain systems containing high concentrations of acidic radical, the rise of Kd in the acidic region was followed by a decline toward higher acidities. Also, in a certain range of acidic radical concentration, when the adsorption was left to equilibrate beyond several hours, the TcOk once adsorbed tended to desorb again, displaced by a coexisting other anion, which caused Kd to relapse with further progress ofequilibration time. The desorption behavior differed with the kind ofactivated carbon, and with the kind and concentration of the acid contained in the system. Pretreatment of the adsorbent with acid devoid of Tc04 resulted in lowering of the adsorption performance.