The complete amino acid sequence of [2Fe-2S] ferredoxin from Nicotiana tabacum has been determined by automated Edman degradation of the entire Cm-protein and of the peptides obtained by trypsin and Asp-N endoproteinase digestions. This ferredoxin exhibited 9, 10, 8, and 10 differences respectively in its amino acid sequence, when compared with the ferredoxins of Datura stramonium, D. metel, D. arborea, and Physalis alkekengi var.francheti but 17-28 differences for other angiosperms, and 34-37 differences for fern and horsetails. These results are in agreement with the taxonomic position for these plants.