Soluble and toxic oligomers of amyloid beta (A beta) protein have been identified as the true neurotoxic species involved in Alzheimer's disease and considering them as targets to inhibit A beta aggregation might have a therapeutic value. We previously set up a CE method that enables the separation and quantification of transient oligomers of A beta protein-containing 42 amino acids (A beta(1-42)) along the pathway leading to fibrils and we now demonstrate how this method can be successfully applied to examine the in vitro inhibitory effects of small molecules on A beta oligomerization. To this end, we investigated mitoxantrone and pixantrone, two well-known anticancer drugs, as well as suramin and a suramin-like compound. By using CE, it is here shown how mitoxantrone and pixantrone either reduce or block A beta(1-42) oligomerization, while Thioflavin T spectrofluorimetric assay and transmission electron microscopy demonstrate how these two compounds also display antifibrillogenic activity. Interestingly, in vitro cell viability experiments indicated that pixantrone significantly reduces A beta(1-42) neurotoxicity.