Electrolytes and/or amino acids were determined in leg skeletal muscle biopsies from elderly (age range 57–75 years) and young (age range 20–35 years) apparently healthy women. When compared to the young group, the elderly one was characterized by increased levels of muscular Na+ and Cl––, while the calculated intracellular concentration of Na+ was reduced. The pattern and levels of free amino acids showed only minor differences between elderly and young women. Intracellular Mg2+ and K+ showed a significant correlation with muscle levels of simultaneously determined energy-rich phosphagen compounds that was published pre