The adsorption behaviour on hydrous manganese dioxide of 99Mo in the form of molybdate and molybdophosphate and of 99mTc in the form of pertechnetate was investigated at different solution acidities. The adsorption capacity of molybdenum is much higher for the molybdophosphate form. A 99mTc-generator is suggested. This generator is based on the adsorption of [ 99Mo]molybdophosphate on MnO 2, at an acidity of 0.5 N. 99mTc is then eluted either by 0.9% NaCl or by methyl ethyl ketone. Radionuclidic, radiochemical and chemical purity tests of the eluates were performed and the present generator seems to offer some advantages over the traditional alumina generator.