The solventextraction of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu from weak acidic chloride solutions into an organic phase containing 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (HP) and phosphoryl-containing podands (L) has been studied. A considerable synergisticeffect was observed in the presence of neutral ligands L in the organic phase containing HP. The stoichiometry of the