The 3-methylhistidine content of human tissues.

1. The amount of 3-methylhistidine (3-MeH) has been measured in eighty-eight samples of tissue taken post-mortem from five adults. 2. The highest concentration (mumol/g fat-free dry weight) of 3-MeH was in skeletal muscle (3.31 +/- 0.05); intermediate values (2-3) were found in cardiac muscle and those tissues containing smooth muscle; and low values (less than 1) occurred in parenchymal tissues such as liver and kidney. 3. There was little variation between the mean 3-MeH content of striated muscles in different individuals, and no significant difference between the 3-MeH concentrations of striated muscles taken from six different sites. 4. The results suggest that it is justifiable to use values obtained from single muscles to calculate the rate of myofibrillar breakdown from urinary 3-MeH excretion.