Plasma amyloid-beta peptide (A beta) levels have been suggested as a biomarker candidate for detecting incipient AD. A beta peptides are known to be sensitive to distinct preanalytical sample handling, which calls for standardised preanalytical procedures. We investigated serum and plasma samples of 19 patients with no clinical signs of dementia for different preanalytical sample handlings. Both serum and plasma were analysed by the one-dimensional A beta-SDS-PAGE/immunoblot, either immediately or after storage at room temperature for 24 and 48?h, respectively. The panel of A beta 137/38/39/40/42 and A beta 240 was evaluated. In both analytical matrices, sample storage led to a significant loss of measurable peptide levels. This effect was most pronounced during the first 24?h of storage and stronger in serum than in plasma. There were no significant differences between the distinct analysed A beta peptide species regarding these results. The ratios of peptides (e.g. A beta 142/A beta 140 and A beta 142/A beta 138) displayed a higher stability under the influence of storage than each single peptide. In conclusion, plasma may be more appropriate than serum for analysing A beta peptides for routine application. At least, the analysis should be done within 24?h and peptide ratios should be created to minimise artificial results.