A method for the direct determination of methemalbumin in serum by means of difference scanning spectrophotometry is described. The advantages of this quantification technique resides in the ability to obviate unequal background characteristics such as turbidity in one treated sample portion, the avoidance of subtractive measurement on the sides of steep spectra, and a qualitative observation simultaneously derived from the single difference scan. A measure of the stability of the prepared standards is described along with a minimized use of sample and reagent volumes if the latter is desired.