We investigated the extraction equilibrium behavior of a series of trivalent lanthanide ions, (M3+), La, Pr, Eu, Ho, and Yb, from tar-trate aqueous solutions using a chloroform solution containing N-p-methoxybenzoyl-N-phenylhydroxylamine (Methoxy-BPHA or HL) combined with an adductant, 1,10-phenanthroline (phen) or 2,2'-bipyridyl (bipy). The synergistic species extracted were found to be {ML2(phen) 2- 2-2(HL)}(+)(1/2)Tar and {ML2(bipy)(HL)2)+(1/2)Tar, where Tar is the tartrate ion. The stoichiometry, the extraction constants, and the separation factors of these systems were determined. We discuss the extractability and the separation factors in comparison with self-adduct chelates, ML3(HL)2,(,), which were formed in the absence of phen or bipy.