Bifidobacterium longum grew at 65 L pilot scale of the membrane bioreactor (MBR), externally fitted with ceramic membrane (0.7 m(2)). Cell mass at the MBR reached 22.18 g L(-1) as dry cell weight in 12 h, which is 8.44 times higher than cell mass attained at the vial culture. The growth rate in the vial culture was mu = 0.385 h(-) and at the batch culture was mu = 1.13 h(-) in the exponential period and mu = 0.31 h(-1) in the stationary period. In the fed-batch mode was mu = 1.102 h(-1) for 6 h with inoculation and declined to mu = 0.456 h(-1) with feeding of feed medium. The growth rate at the MBR was mu = 0.134 h(-1). The number of viable cells was 6.01 x 10(12) cfu L(-1) at the batch culture, but increased to 1.15 x 10(14) cfu L(-1) at the MBR culture. The specific growth rate of viable cell number (colony-forming units per liter, per hour) improved by 6.01 times from the batch to the MBR culture. The wall shear stress mainly generated by the pump, and the membrane incorporated into the MBR was controlled during the cultivation at the MBR. The viability of B. longum declined to under 10% in the first 2 weeks of the 4-week stability test (40 degrees C) as B. longum was exposed to over wall shear stress 713 Pa, but the viability improved to 30-40% in wall shear stress of 260 Pa or STR culture. The loss in the cell viability can be saved by managing with wall shear stress during the cultivation at the MBR.