Broiler chicks were fed normally for 21 d, then starved overnight and given a single oral dose of an aqueous solution of diammonium hydrogen citrate (DAHC), triammonium citrate (TAC), ammonium lactate (AL) or urea equivalent to 24.76 mg N. Controls were given water. The concentrations of free amino acids in the plasma were measured 2, 4 or 6 h after dosing. The only non-essential amino acid significantly affected was glutamine, which increased in chicks given DAHC or TAC (P less than 0.01). In another experiment, non-protein nitrogen (NPN) from the same sources was given at dosages of 124 mg N per chick. The concentrations of free amino acids in the plasma and liver were determined 2, 4 or 6 h after dosing. NPN from all sources increased the amount of glutamic acid and glutamine in both tissues (P less than 0.001), although the response to urea was delayed. The concentrations of plasma aspartic acid (P less than 0.05), plasma alanine (P less than 0.001) and liver aspartic acid (P less than 0.001) also increased. The results are discussed in relation to earlier studies with liver homogenates in vitro.