Sarcopenia is the loss of muscle size and function during ageing. The aim of this study was to test whether serum concentrations of myostatin and interacting proteins (GASP-1, FLRG, and follistatin) differed between young and elderly sarcopenic men. Isometric knee extensor maximal voluntary contraction and quadriceps cross-sectional area (magnetic resonance imaging measurement) were significantly higher in young (22 +/- 2 years; 266 +/- 54 N/m; 8,686 +/- 1,154 mm(2)) than in mildly sarcopenic (69 +/- 3 years; 183 +/- 17 N/m; 6,621+/-718 mm(2)) and severely sarcopenic men (76 +/- 6 years; 127 +/- 23 N/m; 5,846 +/- 591 mm(2)), respectively (p = .01 for all comparisons). There was a trend (p = .06) toward higher FLRG in young (20 +/- 8 ng/mL) than in mildly (15 +/- 6 ng/mL) and severely sarcopenic men (17 +/- 8 ng/mL). Myostatin, follistatin, GASP-1, tumor necrosis factor alpha, and interleukin-6 did not differ significantly. Insulin-like growth factor-1 and free testosterone were both significantly lower in sarcopenic men (p < .001). This suggests that altered serum concentrations of myostatin and myostatin-interacting proteins are not contributing to sarcopenia with the possible exception of FLRG.