Exomaltotetraohydrolase (G4ase) catalyzes the hydrolysis of (1->4)-α-_D-glucosidic linkages in amylaceous polysaccharides from the non-reducing ends removing successive maltotetraose residues. A safety assessment was conducted for G4ase produced by the non-genetically modified strain of Pseudomonas stutzeri, MO-19. Two standardized acute oral toxicity studies using female rats were performed on G4ase having a TOS not determined for the first study and 7.13% TOS for the second. The 50% lethal dose (LD₅₀) of G4ase was determined to be more than 2000 mg/kg, corresponding to more than 143 mg-TOS/kg. A 2-week oral repeated toxicity study in rats at 1000 mg/kg/day (highest dose; TOS not determined) demonstrated no treatment related toxicity and was used to identify the appropriate dose for a 90-day study. Results of a standardized 90-day oral repeated toxicity study (gavage) of G4ase (7.13%-TOS) using rats demonstrated that the No Observed Adverse Effect Level (NOAEL) of G4ase was 1000 mg/kg/day (the highest dose), corresponding to 71.3 mg-TOS/kg. Four standardized genotoxicity studies of bacterial reverse mutation, chromosomal aberration, and in vivo and in vitro micronucleus tests were performed on G4ase (5.19, 5.19, 7.13 and 6.65%-TOS, respectively). It was concluded that G4ase did not induce gene mutation in Salmonella typhimurium and Escherichia coli, did not induce chromosomal aberrations in cultured mammalian cells, and did not induce micronucleated erythrocytes in rat bone marrow cells or human spleen cell line lymphoblasts. Taken together these data indicate that G4ase from P. stutzeri strain MO-19 is safe for use as a processing aid in manufacturing food for human consumption.