Poly(propylene imine) dendrimers having 8, 32, and 64 primary amine end groups (D8, D32, and D64) form Cu(II), Zn(II), and Co(III) complexes that are identified spectrophotometrically. Solutions of D32 containing 2 or 4 primary amine groups per metal ion catalyze the hydrolysis of bis(p-nitrophenyl) phosphate in unbuffered NaClO4 solutions at 45 degrees C with rate maxima at pH 6.6-7.25. The observed rate constants for all 3.0 mM Co(III) and Cu(II) complexes were about 7.10(-5) s(-1), and for 1.5 mM Zn(II) at 2 NH2/Zn was 6.10(-5) s(-1). The results are consistent with the accepted mechanisms of electrophilic metal ion catalysis of hydrolysis of phosphate diesters by nucleophilic attack of metal-bound hydroxide ion on bis(p-nitrophenyl) phosphate.