The equilibrium extraction behavior for a series of trivalent lanthanide ions, La, Pr, Eu, Ho and Yb, using chloroform solutions containing N-benzoyl- phenylhydroxylamine ( BPHA ) , either alone or combined with 1 ,10-phenantholine ( phen ) , trioctylphosphine oxide (TOPO) or tetra-n-heptylammonium chloride (R_4NCl) was studied. The results demon strated that these lanthanides are extracted as Ln (BPHA) 3 -BPHA, or in the presence of phen, as Ln ( BPHA )3.phen , or in the presence of R4NCL, as R4N L n ( BPHA )4 . However, in the presence of TOPO no adduct formation occurs.