Density measurements of aqueous albumin solutions as a function of concentration and temperature are reported. The solvents were H2O, D2O, and a physiological H2O-based buffer, An anomaly of the density at very small concentrations of albumin in D2O was found. Furthermore, the partial specific volume of albumin is remarkably different in D2O and H2O, We attribute both effects to structural differences of the solvents.