Proton-induced gamma-ray emission (PIGE) analysis has been applied to the determination of total nitrogen concentration of blood sera from hospital patients. Both the reaction14N(p,p)14N,E= =2313 keV, and the reaction15N(p,)12C,E=4439 keV, have been used. From 37 patients, the range of the nitrogen concentrations obtained was 9.54–16.3 g/l with a mean of 12.0 g/l. The corresponding total protein concentrations varied between 59 and 96 g/l, measured in a clinical laboratory autoanalyser using the biuret method. The range of the albumin concentrations was 29–46 g/l. The nitrogen concentrations correlated well with the total protein concentrations (r=0.802). The multiple correlation of nitrogen versus (albumin+(total protein-albumin)) gives a coefficient of 0.175 for albumin and 0.161 for total protein-albumin. The results agree with expectations and support the potential usefulness of the rapid PIGE method for medical studies.