The amino acid sequences of two ferredoxins isolated from pokeweed, Phytolacca americana, were determined. Tryptic peptides of maleyl-carboxymethyl-ferredoxin I and carboxymethyl-ferredoxin II were prepared and analyzed. The large peptides were further digested with staphylococcal protease and chymotrypsin. Ferredoxins I and II were composed of 96 and 98 amino acid residues, respectively. Though ferredoxin I lacks tryptophan and methionine, ferredoxin II contains both of them. In a comparison of the amino acid sequences with those of other higher plant ferredoxins, ferredoxin I is one residue shorter than others at the carboxyl-terminus and ferredoxin II one longer than others at the amino-terminus. Ferredoxins I and II differ in 23 sites from each other and in 27 to 37 sites from other higher plant ferredoxins. This suggests that duplication of the ferredoxin gene occurred after the divergence of pokeweed from other higher plants. A phylogenetic tree including all other ferredoxins was constructed.