Rhizobium spp. show chemotaxis to plant root exudates. Both legumes and non-legume root exudates attract the different rhizobia studied. However, the bacteria show a differential response in that they are attracted to the root exudates of some plants and show no attraction toward others. An example of negative chemotaxis was also observed. The trefoil strain of Rhizobium shows chemotaxis which is qualitatively different from that observed in other bacteria in that simple sugars, di-and trisaccharides, dextrans, and amino acids do not attract this bacterium.