A kinetic modeling of leucine plasma concentration changes is proposed to desc ribe the plasma leucine reduction rate during continuous extracorporeal removal therapy (CECRT) in neonates with mapl e syrup urine disease. Data were obtained from seven neonates using a bicompartm ental model for the best fitted curve of plasma leucine decrease during CECRT. D uring the first 3 h, leucine plasma levels decreased according to an exponential curve: [Leu]t = [Leu]i ×0.95 ×10-0.09t where [Leu] t is the leucine plasma l evel (μmol/L) at time t (h) during CECRT and [Leu]i is the initial plasma level . From h 4 to the end of CECRT, a second exponential curve was observed: [Leu]t = [Leu]i ×0.74 ×10-0.05t. Plasma leucine levels obtained from three other neo nates were similar to those predicted by the model. The apparent distribution vo lumes for leucine that correspond to the two exponential equations obtained were calculated from the leucine mass removal collected in the spent dialysate and u ltrafiltrate. The distribution volume was 34 ±3%of body weight during the firs t 3 h of CECRT and 72 ±7%from h 4 to the end of CECRT. These figures are simil ar to known values for the extracellular water compartment and for total body wa ter in the newborn. The findings suggest that leucine handling during CECRT is s imilar to that of nonproteinbound small-molecular-weight solutes such as urea. A kinetic modeling of leucine plasma concentration changes is proposed to desc ribe the plasma leucine reduction rate during continuous extracorporeal removal therapy (CECRT) in neonates with mapl syrup urine disease. Data were obtained from seven neonates using a bicompartm ental model for the best fitted curve of plasma leucine decrease during CECRT. D uring the first 3 h, leucine plasma levels decreased according to an exponential curve: [Leu] t = [Leu] i × 0.95 × 10 -0.09 t where [Leu] t is the leucine plasma Leh] i is the initial plasma level. From h 4 to the end of CECRT, a second exponential curve was observed: [Leu] t = [Leu] i × 0.74 × 10-0.05t. Plasma leucine levels obtained from three other neo nates were similar to those predicted by the model. The apparent distribution vo lumes for leucine that correspond to the two exponentialystems obtained were calculated from the leucine mass removal collected in the spent dialysate and The distribution volume was 34 ± 3% of body weight during the firs t 3 h of CECRT and 72 ± 7% from h 4 to the end of CECRT. These figures are simil ar to known values ​​for the extracellular water compartment and for total body wa ter in the newborn. The findings suggest that leucine handling during CECRT is s imilar to that of nonproteinbound small-molecular-weight solutes such as urea.