Nagase analbuminemic rats (NAR) are deficient in serum albumin. Extravascular regions of the tissues of NAR were tested for rat serum albumin by the immunofluorescence staining technique. Albumin was not detectable in any of the tissues of NAR tested (liver, kidney, muscle, skin, and small intestine), whereas it was clearly demonstrated in all these tissues of normal rats. Furthermore, extracts of NAR tissues, including the liver, contained no albumin detectable by the single radial immunodiffusion method. These findings indicate that albumin is not present in either the serum or extravascular regions of tissues of NAR, and suggest that the deficiency of serum albumin in NAR is not due to impaired albumin secretion from the liver or alteration of the tissue distribution of albumin in certain tissues, but to the absence of its synthesis in the liver.