A distinctive feature of Alzheimer’s disease is the deposition of amyloid -protein (A) in senile or diffuse plaques. The 42 residue -peptide (A42) is the predominant form found in plaques. In the present work we report a high-yield expression and purification method of production of a recombinant A42. The purified recombinant peptide shows characteristics similar to the synthetic human peptide. Different size aggregates, either small oligomers or larger aggregates, were obtained upon dissolving the recombinant A42 peptide under different conditions at pH 7.2 or pH 3, respectively. We report a new toxicity assay on the morphogenic development of the sea urchin Paracentrotus lividus and study the toxicity of the two kinds of aggregates. Despite the difference between the ionic strength of human extracellular fluid (0.154 mol/l) and artificial sea water (0.48 mol/l), toxicity data collected in this system have an intrinsic relevance. The different ionic strength, in fact, could change the kinetics of oligomer formation, but the effect of morphogenic development reported here is related to the final oligomer sizes. Results of the toxicity assay of A42 on sea urchin development also show a dose-dependent effect. After only 4 h of embryo development, one can note morphological defects in the cell membrane. Retardation of the embryo’s development, along with cellular disorders visible inside the blastocoele, can be observed after 1 day of development. Cellular degeneration in two different pathological phenotypes--the occluded blastulae and the occluded prism--is present after 48 h of development. Results show that a greater effect on cell death is induced by the small oligomers stabilized under physiological conditions than at acid pH. In this case only occluded blastulae are found after 48 h of development.--Carrotta, R., Di Carlo, M., Manno, M., Montana, G., Picone, P., Romancino, D., San Biagio, P. L. Toxicity of recombinant -amyloid prefibrillar oligomers on the morphogenesis of the sea urchin Paracentrotus lividus.