In the distribution of their serum groups the totality of 48 patients with paranoid psychoses of late onset is characterized by failure of the well-known markers of manic-depressive or schizophrenic illness. However, when differentiated psychopathologically, the haptoglobin (Hp) type 2–2 as a risk factor of cyclothymic psychoses is found to be significantly overrepresented in the patient group with a cyclic axis syndrome. On the other hand, an excess of Hp 1–1 can be observed and statistically confirmed in comparison with the population level among the patients offering a schizophrenic axis syndrome or resting unclassified. Possibly, the Hp serum groups play a role in the bioregulation of emotionality. The ‘noncyclic’ group does not show the marker traits of process psychoses, but in this sampüng there is, in contrast to the ‘cyclics,’ a higher concentration of the immunoglobulin G serum level on the statistical border line, which perhaps is caused by destructive factors. The results correspond with the special state of the examined psychoses basing on biological determinants of diff