Previous research has indicated that reduced expression of elongation factor-1 alpha (EF-1 alpha) may be an important determinant of the reduced rate of protein synthesis in senescent animals and cultured cells. The present study examined whether expression of EF-1 alpha or S1, a homologous protein found exclusively in postmitotic tissues, is reduced in senescent human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis muscles of healthy young (22-31 yr old) and old (61-74 yr old) subjects. As reported previously, myofibrillar protein synthesis was approximately 40% slower in the older muscle (p < .001) as determined by incorporation of a stable isotope. Immunoblotting revealed no difference in the concentration of EF-1 alpha + S1 between younger and older muscle. RT-PCR assays indicated that S1 mRNA was much more abundant than EF-1 alpha mRNA in muscles of both age groups, with no reduction in either EF-1 alpha or S1 mRNA abundance in older muscles. We conclude that expression of EF-1 alpha and S1 is not diminished in older muscles and does not explain the age-related slowing of protein synthesis in human skeletal muscle. However, we cannot exclude the possibility that the activity of these proteins declines during senescence due to post-translational modifications.