The concentrations of 24 amino acids and four other related compounds were determined in extracts of biopsy specimens from myometrium and musculus rectus abdominis of 10 healthy term pregnant women during elective cesarean sections. The total free amino acid pool did not differ significantly between the two muscle types. There was a myometrial abundance of the two anionic amino acids glutamate and aspartate and the two aromatic amino acids tyrosine and phenylalanine, but most neutral and cationic amino acids in striated skeletal muscle tissue were found in excess of those in uterine muscle tissue.