In 13 subjects with different body weight, the body density was assessed by hydrostatic weighing and the metabolism and distribution of albumin labelled with radioactive iodine. Between the amount of thus estimated lean body mass (LBM) and parameters of albumin metabolism, important correlations were found. The relationship of albumin catabolism and amount of LBM is significant (r = +0.6494; 0.05 > p > 0.01), similarly as the relationship between total albumin and LBM. It is of interest that between 20 and 40 years there is a continuous decline in the catabolic rate of albumin per unit of LBM and thus the decline of the metabolic rate is not mediated by the changing ratio of body fat. It was demonstrated that the lean body mass is also the most suitable reference standard for the evaluation of albumin metabolism.