AbstractComparisons of the physiology and kinetics of protein turnover, i.e. protein synthesis and degradation, in different animal species (rats, sheep, pigs and cattle) including man, are presented. Also, the effects of food on protein turnover in tissues, including responses to a meal, starvation and protein deprivation, are discussed. The effects of hormones on tissue protein turnover are discussed as well; the hormones studied include insulin, insulin-like growth hormone, thyroid hormones and glucocorticoids.