Some combinations of extractants involving dicarbollide as one component for the separation of Am/Ln were studied. Extraction by TOPO is not influenced to a great extent by the presence of dicarbollide, and TPTZ in the presence of dicarbollide is ineffective for the extraction from 0.1 M HNO3. General aspects of the selectivity of lanthanides and of Am/Ln separation in the presence of various reagents are discussed with emphasis on the difficulties of the separation of Am from light lanthanides. A new extraction procedure by dicarbollide in the presence of an excess of o-phenanthroline over the mineral acid is proposed. This led to the highest separation factors D(Am)/D(Eu) (20-34) from 0.1 M HNO3. The behavior of other lanthanides is similar to that of Eu, with a maximum distribution ratio for Nd (D(Nd)/D(Eu) = 2).