The chemotaxis of Salmonella typhimurium LT2-ST1, grown with different sole carbon sources toward ribose, allose, serine, aspartate, and glucose, was examined. Maximum chemotaxis toward serine, aspartate, and glucose were unchanged with either glucose or citrate as the carbon source. The height of the peak in the ribose response curve was 25% of a standard serine response when the bacteria were grown on citrate. However, when the bacteria were grown on glucose, the ribose response was 1% of the serine standard, and when on glycerol, 5%. Chemotaxis toward allose, a competitive inhibitor of ribose chemotaxis, was similarly affected. The amount of ribose binding protein, the receptor for ribose chemotaxis, was determined in bacteria grown on citrate, glucose, or glycerol. The amount of ribose-binding protein released from cells grown on glucose or glycerol was appreciably less than the amount released from cells grown on citrate. These data suggest that the observed effect on ribose chemotaxis is due to catabolite repression of ribose-binding protein and another component of the chemotactic system.