Small heat shock proteins Hsp20 and HspB2/B3 co-localize with Abeta deposition in senile plaques and cerebral amyloid angiopathy in Alzheimer's disease brains, respectively. It was the aim of our study to investigate if these and other sHsps bind to wild-type Abeta1-42 or the more toxic Abeta1-40 carrying the 'Dutch' mutation (22Glu-->Gln) (D-Abeta1-40), affect Abeta aggregation and thereby influence Abeta cytotoxicity. Binding affinity between sHsps and Abeta was investigated by surface plasmon resonance. Abeta aggregation was studied by using circular dichroism spectroscopy and electron microscopy. Furthermore, we used cultured cerebrovascular cells to investigate the effects of sHsps on Abeta-mediated cytotoxicity. Hsp20, Hsp27 and alphaB-crystallin, but not HspB2/B3, bound to Abeta (both D-Abeta1-40 and Abeta1-42) and reduced or completely inhibited aggregation of D-Abeta1-40 into mature fibrils but did not affect Abeta1-42 aggregation. Furthermore, these sHsps were effective inhibitors of the cerebrovascular toxicity of Abeta (both D-Abeta1-40 and Abeta1-42) in vitro. Binding affinity of the sHsps to D-Abeta1-40 correlated to the degree of inhibition of Abeta-mediated cytotoxicity and the potential to reduce Abeta beta-sheet and fibril formation. With Abeta1-42, a similar correlation between binding affinity and cytotoxicity was observed, but not with its aggregation state. In conclusion, sHsps may regulate Abeta aggregation and serve as antagonists of the biological action of Abeta, but the extent of their interaction depends on the type of sHsp and Abeta peptide.