Serum amyloid P component (SAP) binds to all amyloid fibrils including those in the plaques and tangles of Alzheimer patients. To investigate whether the plasma SAP concentration correlated to cognitive impairment, we measured SAP levels in blood samples from 41 centenarians and compared these to the cognitive performance evaluated by Mini Mental State Examination (MMSE). We observed a significantly (p < 0.001) increased SAP concentration (48.3+/-16.9 microg/ml; mean +/- SD) in the centenarians compared to gender-matched controls (32.8+/-11.4 microg/ml). Six severely demented centenarians had an even higher SAP concentration (60.2 microg/ml), while the subgroup of cognitive intact centenarians (MMSE score >24) showed a normal SAP concentration (38.4+/-9.3 microg/ml). No dehydration or hepatic dysfunction was demonstrable in the centenarians. We conclude that the centenarians with impaired cognitive performance had significantly increased plasma concentrations of SAP, while the values for cognitive intact centenarians were within the normal range.