To determine the extent to which chemotactic behavior depends on methylation at multiple sites, chemotaxis assays were performed on bacteria that expressed mutant aspartate receptors in which methylation site residues were mutated from glutamate to aspartate. It was found that chemotaxis was impaired when methylation sites were mutated and that the effect on chemotaxis of mutating a rapidly methylated site was more severe than the effect of mutating a less-rapidly methylated site. Expression of mutant receptors in a wild-type strain interfered with chemotaxis to only a minor extent. In vivo methylation assays showed that the chemotactic defects of most mutants could be explained by the decreased rates at which methylation levels increased in response to aspartate.