By means of a double chromatographic separation technique applied to the acid fraction of methanol extracts of root nodules, parental roots, and 14 day old roots of Lupinus luteus L., indoleacetic acid and indolecarboxylic acid were demonstrated spectrofluorometrically and the amounts determined. The difference between the IAA content of nodules and parental roots on a fresh-weight basis was not as great as is generally believed: we found about 3 times more IAA in nodules than in roots. The 14 day old roots contained the lowest amount of IAA: about half the amount found in roots on which nodules had been present. The ICA content of roots that had been in contact with nodules was about 3 times higher than the ICA content of the nodules. The ICA content of 14 day old roots was the lowest. These results are discussed in the light of a possible alteration of the indole metabolism of the root caused by infection with the bacterial symbiont Rhizobium lupini, as an indication for a fundamental alteration of growth-regulation leading to the genesis of nodules.