The addition of glucose to an Escherichia coli culture causes a transient but strong Inhibition of synthesis of many inducible catabolic enzymes (transient repression). This is followed by a weak but permanent repression (catabolite repression). In order to study how glucose causes such repressions, mutants which are resistant to transient and/or catabolite repression may be useful. A method has been developed for isolating such mutants from a motile strain of E. coli by making use of the fact that glucose also represses the synthesis of its flagella, thus inhibiting motility. The addition of gluconate is known to intensify glucose repression, therefore, mutants were selected which were able to swim towards a chemotactic attractant even after growth in glucose and gluconate. Most of these mutants were able to produce /3-galactosidase in the presence of glucose, and were normal in their ability to degrade adenosine 3»5-cyclic monophosphate (cAMP). The characterization of six independently isolated mutants indicates that they exhibited no catabolite repression of B-galactosidase, but varying degrees of transient repression. This is correlatable with their ability to transport oi-methylglucoside via the glucose phosphotransferase system. It has been suggested that cAMP may mediate transient and catabolite repression and that ATP may be the catabolite responsible for catabolite repression. However, the intracellular concentrations of cAMP and ATP did not fluctuate when glucose was added to glycerol-grown cultures of the mutants or the wild type. This suggests that some, as yet unknown factor, also contributes to transient and catabolite repression. The present isolation method has the potential to yield a greater variety of glucose repression-resistant mutants in contrast to previous methods which enrich for a limited variety of such mutants.