Investigations of the effects of glutamic acid or its salts on the flavor, hedonic characteristics or acceptance of foods have emphasized a sodium salt of L-glutamic acid, monosodium glutamate (MSG). Food palatability increased with appropriate concentrations of MSG, and could be represented f(MSG and NaCl) as points on the surface of an elliptic paraboloid. Hedonic effects differed between foods, were a function of concentrations of MSG and other ingredients and did not necessarily become positive when only MSG was added. For example, with boiled or fried rice, ratings were neutral or negative with MSG alone, positive for fried rice with MSG and NaCl, but positive for boiled rice only if soy sauce was also added. A one-dish meal, Chinese noodle, became positive with an appropriate concentration of NaCl plus a MSG-5'ribonucleotide mixture, but not with NaCl alone. Flavor of meat, fish or vegetable stocks containing natural glutamates differed from that of quinine, sucrose, NaCl or acid solutions. Glutamates and free amino acids plus nucleotides were necessary for full boiled potato flavor. Overall, the effects of MSG on foods were different from those of NaCl but often interacted with NaCl, and positive effects were facilitated by low concentrations of 5'-ribonucleotides.