Cells of Campylobacter concisus 288 were chemotactic toward formate, but not to any other compound tested. Chemicals that were not chemoattractants included 20 sugars, inorganic salts, amino acids, and their derivatives, purines and pyrimidines, fatty acids, and natural mixtures such as saliva, serum, crevicular fluid, and mucin. Chemotaxis was measured quantitatively by a modification of the capillary method. Cells were suspended in 0.01 M Tris buffer, pH 7.5, supplemented with 5 mM KCl, 0.1% Na2S2O3, and 0.1 mM dithiothreitol. Whole, parotid, and submandibular salivas were also suitable as chemotaxis buffers. Optimum response (0.4 X 10(6) to 1.5 X 10(6) cells per capillary) for chemotaxis occurred with 5 X 10(-2) M formate at 30 degrees C for 60 min. At 5 to 15 degrees C, cells were motile, but chemotaxis was not detected. Glutamine, asparagine, homoserine, and methionine inhibited formate chemotaxis at threshold concentrations of 0.1 to 1.0 mM, whereas the threshold for all other amino acids tested was 50 mM. Sugars and fatty acids at concentrations up to 0.1 M did not inhibit formate chemotaxis. C. concisus 484, Wolinella recta 371, W. curva VPI 9584, and W. succinogenes 602 were also chemotactic to formate, but C. fetus subsp. jejuni VPI H641 and C. fetus subsp. intestinalis VPI 1176 were not. Motile bacteria harvested directly from subgingival plaque were also chemotactic to formate and, to a lesser extent, lactate. Selected sugars, other fatty acids, and amino acids did not serve as chemoattractants for these plaque bacteria.