The amyloid fibrils of amyloid beta protein (A beta) from Alzheimer's disease are likely to show the cytotoxicity, depending on their morphology. The relationship between the nucleation kinetics of the A beta fibrils and their morphology has been investigated. From the perspective of a crystallization technique assuming primary/secondary nucleation steps and an elongation step, the secondary nucleation rate B [# m-3 s-1], was experimentally and coarsely determined by using total internal reflection fluorescence microscopy combined with thioflavin T. In an aqueous solution, linear and rigid fibrils were formed with a relatively smaller B value ((2.83 +/- 0.55) x 105 # m-3 s-1), whereas spherulitic amyloid assemblies were formed in the presence of negatively charged liposome including oxidized lipids, with a larger B value ((7.65 +/- 0.47) x 105 # m-3 s-1). Those findings should lead to a better understanding of the mechanism for the formation of fibrils and senile plaques in Alzheimer's disease. (C) 2012 American Institute of Chemical Engineers AIChE J, 2012