The sound speed and the density of a series of blood samples was measured in a temperature range from 20 degrees C to 40 degrees C. An expression was derived from a least square fit which related the sound speed in human blood in this temperature range to the blood density and to the total protein concentration, respectively. The data were obtained from the measurement of sound speed and density by means of a newly developed Density and Sound Analyzer (DSA-48, A. Paar K.G., 8054 Graz, Austria). The relationship of sound speed, density and temperature permits the calculation of the total protein concentration with an accuracy of 1 g/kg. The resolution of the measurement is in the order of 0.1 g/kg.