A serum has been studied, in which direct observation of cellulose acetate electrophoresis may induce misdiagnosis of analbuminaemia. Immunogically, and by saline fractionation, the serum contained albumin, although in a decreased quantity. Gel filtration shows the majority of this albumin is to be in the 4.5 S20 peak and to have a low electrophoretic mobility, overlapping with that of alpha 1 globulins. Possible explanations of the presence of this slow-moving albumin are discussed.