The Sparkle/PM3 model is extended to praseodymium(III), and ytterbium(III) complexes. The same two sets of 15 complexes used to parameterize Sparkle/AM1, were used as training sets. The validation procedure included additional high quality crystallographic structures for a total of 48 structures of Pr(III) complexes, and 47 Yb(III) complexes. The Sparkle/PM3 unsigned mean error (UME), for all interatomic distances between the trivalent lanthanide ion and the ligand atoms of the first sphere of coordination is 0.09 angstrom for Pr(III); and 0.08 angstrom for Yb(III). These figures are similar to the Sparkle/AM1 ones of 0.08 angstrom, and 0.08 angstrom respectively, indicating they are all comparable pararneterizations. (c) 2007 Elsevier BN. All rights reserved.