The purpose was to study whether the kidneys eliminate inactive renin from the circulation of mice. The urinary concentration, excretion rate and clearance of inactive renin were very low during basal conditions. After blockade of the reabsorption of proteins in the renal tubules with the basic amino acid lysine, the urinary concentration, excretion rate and clearance of inactive renin increased very markedly. This finding indicates that inactive plasma renin is subjected to glomerular ultrafiltration followed by reabsorption in the renal tubules by mechanisms which are most likely the same as for active renin and other filtered proteins. The urinary clearance of inactive renin after blockade of the renal tubular protein reabsorption was 13% of that of active renin. Our findings demonstrate that glomerular ultrafiltration is a route of elimination from the circulation for inactive renin.