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1. The rate of elimination of administered Nτ-[14CH3]methyl histidine was used to assess the validity of Nτ-methyl histidine excretion as an index of muscle protein breakdown in poultry.2. Broiler chicks (2–3 and 4–5 weeks old), laying hens, adult quail (Coturnix coturnix japonica), adult cockerels and turkey poults (2–4 weeks old) were tested.3. All except the turkey poults showed quantitative recoveries of Nτ-[14CH3]methyl histidine within 1 week.4. Turkeys showed a different pattern of Nτ-[14CH3]methyl histidine output; the mean total recovery after 14 d was less than 50% of the injected dose. The majority of the label remaining after this time was found in breast muscle.5. All birds tested excreted Nτ-methyl histidine unchanged, although a small amount sometimes appeared as another metabolite.6. No significant oxidation of Nτ-[14CH3]methyl histidine by broiler chicks, turkey poults or adult quail was found.7. The results show that excretion of Nτ-methyl histidine is a useful measure of muscle protein breakdown in the domestic fowl and quail but not in turkeys.

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