In growing pigs, improving the efficiency of protein utilization by genetic selection would allow reducing the competition for protein sources between animal productions and other uses. It would also contribute to decreasing nitrogen excretion. The objective of this study was to evaluate the genetic variability of the efficiency of protein utilization in Large White (LW) pigs by quantifying the growth response to varying level of dietary protein. Sixty barrows, descendants from 9 poorly related LW boars and 17 LW x Landrace sows were offered diets supplying 85, 75 or 65% of the estimated requirements for lysine and protein. Feed allowance, equalized between pigs and slightly below the ad libitum level, and dietary protein level were adjusted each week. The test period started at 25 kg and lasted up to 15 weeks (until approximately 95 kg). Reducing the protein and lysine content resulted in a reduction in growth rate (750, 715 and 620 g/d for pigs receiving 85%, 75% and 65% of the estimated requirements respectively) and an increase in backfat thickness at slaughter (15.9, 17.4 and 19.2 mm, respectively). The sire had no effect on the efficiency of protein utilization, nor was the interaction between sire and protein content. Based on these results, the genetic variability in the efficiency of protein utilization seems insufficient to consider selection on this trait.