Fusarium oxysporum f. lupini has been shown to grow in media with one or more amino acids as the only source of carbon. Growth, however, was usually less than in equimolar solutions of sugar. Particular attention was given to the importance of aspartic acid, glutamic acid, asparagine, alanine and leucine. The three latter substances proved to be rather unsuitable substrates for this fungus, although it is possible that some factor essential for their utilization is lacking in these experiments, as must be the case for glutamic acid. Aspartic acid became toxic in concentrations of about 0.1 M. The minimal concentration allowing growth, was shown to be about 0.0125 M. The disadvantages of a low concentration could not be compensated for by greater quantities of the diluted solution. Comparing the results with the data known about the presence and concentration of amino acids in the xylem vessels of lupins we must conclude that these substances cannot be very important for the development of Fusarium in the xylem vessels.