Summary:Serum levels of α1-antichymotrypsin (α1-ACT), macroglobulin, α1-antitrypsin, ceruloplasmin, acid glycoprotein, transferrin, and C-reactive protein were measured in patients with probable late onset dementia of Alzheimer type (1-AD), patients with vascular dementia (VD), healthy elderly (HC), and patients with chronic or acute inflammation. Three blood samples were taken at 10-15-day intervals. Serum α1-ACT levels from first and second serum samples were elevated in one out of 11 1-AD patients. Serpin serum levels from the third sample were increased in four out of 11 1-AD patients. None of these patients showed increased levels of other acute phase proteins measured in the three serum samples. VD patients did not show abnormal serum levels of α1-ACT. Serum levels of α1-ACT along with those of other acute phase proteins were altered in patients with inflammation. This investigation showed that in 1-AD patients with increased α1-ACT and no concomitant elevation of other acute phase proteins, serum levels of α1-ACT varied with time. Based on our results, serum α1-ACT does not appear to be a useful biomarker for clinical diagnosis of probable 1-AD, but it might be associated with the clinical history of the disease