Free amino acids were determined quantitatively in tear fluid and serum samples from the fasting blood of 21 healthy men (aged 22-45 years) and 22 women (aged 21-56 years). Protein was removed from tears and serum by adding an equal volume of 5% sulfosalicyclic acid, and the amino acids were separated by ion exchange column chromatography. None of the 43 subjects showed any evidence of liver damage, kidney or metabolic disease. Men had significantly higher valine, isoleucine and histidine concentrations than women. The range of normal values was determined from these findings.