In batch cultures, Bifidobacterium longum SH2 has a higher final cell concentration and greater substrate consumption when grown on lactose versus glucose. Continuous cultures were used to compare lactose and glucose utilization by B. Longum quantitatively. In the continuous culture, the estimated maintenance coefficients (m) were similar when on lactose and glucose; the maximum cell yield coefficient (Y-X/S(max)) was higher on lactose; and the specific consumption rate of lactose (q(S)) was lower than that of glucose. Assuming that cell growth followed the Monod model, the maximum specific growth rates (mu(max)) and saturation constants (K-S) in lactose and glucose media were determined using the Hanes-Woolf plots. The respective values were 0.40 h(-1) and 78 mg/L for lactose and 0.46 h(-1) and 697 mg/L for glucose. The kinetic parameters of the continuous cultures showed that B. longum preferred lactose to glucose, although the specific consumption rate of glucose was higher than that of lactose.