Media from thein vitroassociation of wheat andAzospirillum lipoferumand from wheat plants alone proved to be chemotactically active. Medium from wheat plants showed a higher attraction than medium from the association. The main attractants were sucrose, glucose, and fructose. In mineral medium without any added sugars, and in association medium with sucrose supplied, and from wheat roots alone, a sucrose excretion and an active invertase were detected. By cleaving sucrose the chemotactic potential increased. Sucrose can not be metabolized byA.lipoferum, whereas glucose and fructose are. Utilization of glucose and fructose by the bacteria may explain why medium from the association wheat–Azospirillumwas less chemotacticaly active than medium from wheat plants alone. Cleavage of sucrose has the additional effect of providing energy sources for bacterial growth and dinitrogen fixation.