Apoprotein SAA is analyzed from the aspect of its function of a general reactant of the acute stage--an indicator of the laboratory activity. The authors give general characteristics of this protein incl. the incidence and probable genesis of different isotypes. On several examples he demonstrates the lack of dependence between the incidence of isotypes and the development of amyloidosis or the basic pathological cause leading to laboratory activity. The simple relationship between the circulating precursor of SAA protein and the deposited AA amyloid fibrils is not unequivocal. Factors leading to the deposition of amyloid are, however, mentioned only liminally. The author discusses in more detail the induction of SAA protein formation at the level of genetic information which makes possible a potent acute response expressed by a rapid and brisk rise of plasma levels.