In this study the effect of protein intake (12% and 21% of total energy intake, diets A and B, respectively) on nitrogen balance and on whole-body protein turnover (PT) was measured in 17 elderly men and 11 elderly women (mean +/- SD: 74 +/- 12 y and 68 +/- 9 y, respectively) with different levels of physical activity. Mean (+/- SD) nitrogen balance (diet A: -0.004 +/- 0.027 g.kg-1.d-1, diet B: 0.011 +/- 0.064 g.kg-1.d-1) did not differ significantly from zero during either diet. PT increased significantly when the protein content of the diet increased from 12% to 21% of total energy (P < 0.0001). There was a positive correlation between protein intake and PT (diet A: synthesis and breakdown, P < 0.01; diet B: synthesis, P < 0.001; breakdown, P < 0.0001). PT rates were significantly higher for men when compared with women, even when corrections were made for differences in body composition (P < 0.05).