In response to infection by the rust pathogen Uromyces fabae the different tissues of broad bean (Vicia faba L.) showed varied pattern of amino acid metabolism; some of them being exclusively present in a particular region only. In the inflorescence tissue, for example, tryptophan, glycine, aspartic acid, serine, proline, and arginine were present. In the stem, however, the amino acids, present during and after infection, were tryptophan, serine, glutamine, homoserine, and dl-alanine. Post-infectionally induced amino compounds, lysine, histidine, vomoserine, proline, tyrosine and dl-threonine, were found in the leaves; in the petiole serine and histidine were the only two such amino acids. Out of these amino acids only histidine and proline, with their specific presence and activity, encouraged uredospore differentiation. L-cysteine, too, by being actively utilized, served as promoter of uredosporulation. Asparagine and methionine showed moderate to heavy depletion during bean tissue infection. On the other hand, l-leucine/isoleucine, beta-alanine, valine, and glutamic acid showed moderate to pronounced increase during pathogenic establishment. Concomitant to uredospore differentiation there was a drastic lowering in the amount of sucrose in leaf and petiole tissue. The amount of glucose also declined during pathogenesis.