Low molecular weight oligomers of amyloid beta (AD) are important drivers of Alzheimer's disease. A decrease in A beta monomer levels in human cerebrospinal fluid (CSF) is observed in Alzheimers' patients and is a robust biomarker of the disease. It has been suggested that the decrease in monomer levels in CSF is due to the formation of All oligomers. A robust technique capable of identifying All oligomers in CSF is therefore desirable. We have used fluorescence correlation spectroscopy and a five Gaussian distribution model (5GDM) to monitor the aggregation of A beta(1-42) in sodium phosphate buffer and in artificial cerebrospinal fluid (ACSF). In buffer, several different sized components (monomer, oligomers, protofibrils and fibrils) can be identified simultaneously using 5GDM. In ACSF, the faster kinetics of fibrillogenesis leads to the formation of fibrils on very short timescales. This analysis method can also be used to monitor the aggregation of other proteins, nanoparticles or colloids, even in complex biological fluids. (C) 2014 Elsevier Inc. All rights reserved.