1. After ingestion of up to 1–2 g of protein/kg body weight by adults, plasma concentrations of all amino acids, including glutamine and glutamic acid, rose to a maximum within 5 h.
2. The increases in concentration depended on the amount of protein ingested.
3. The changes were not due to diurnal variation in plasma amino acid levels, so, protein loading tests may be of value in the assessment of protein absorption.