The relationship between cyclic adenosine 3',5'-monophosphate (cyclic AMP) metabolism and the induction of tryptophanase and beta-galactosidase was studied in several strains of Escherichia coli grown with succinate, acetate, glycerol, or glucose as the carbon source. No consistent relationship between the intracellular concentration of cyclic AMP in the several strains cultured and the various carbon sources was discerned. In E. coli K-12-1 the induction of tryptophanase was found to vary in the order: succinate greater than acetate greater than glycerol greater than glucose, and that of beta-galactosidase was found in the order: glycerol greater than acetate greater than succinate greater than glucose. Rate of accumulation of cyclic AMP in the culture filtrate was in the order: succinate greater than acetate greater than glycerol greater than glucose. The addition of glycerol to E. coli K-12-1 grown in acetate caused inhibition of tryptophanase and slight inhibition of accumulation of extracellular cyclic AMP. These same conditions caused beta-galactosidase induction to be stimulated. The addition of exogenous cyclic AMP to cultures grown with four different carbon sources had an effect characteristic for each of the two enzymes studied as well as each individual carbon source. The results suggest that there are control elements distinct from cyclic AMP and its receptor protein which respond to the catabolic situation of the cell.