Enterobacter sakazakii is the new species name introduced in 1977 for yellow-pigmented strains originally designated as yellow Enterobacter cloacae. All of the six E.sakazakii strains isolated from powdered milk specimens were found to produce Tween 80 esterase after 7 days of incubation at 25 degrees C and 37 degrees C. From E.cloacae it is distinguishable by reactions in four, or even three, biochemical tests, i.e. by production of yellow pigment, positive production of Tween 80 esterase and by non-fermentation of sorbite and mucate; from the Serratia species it can be differentiated by the negative test for lecithinase production.