Vitellogenin induced by estrogen administration has been purified from the serum of Xenopus laevis. Six days after hormone injection, serum was collected and treated with 35% sat. (NH4)2SO4 to remove globulins. A single vitellogenin containing fraction was isolated by chromatography on a Mono-Q column. The protein was identified on the basis of its amino acid composition. N-terminal sequence analysis and SDS-PAGE demonstrated the presence of two forms of vitellogenin (A and B). Consistent with the conclusions drawn from the teratology which chelating agents induce in frog embryos (1), metal analysis shows that vitellogenin is a zinc protein with 1 g atom zinc/220 kDa monomer but containing no other IIB and transition metals.