In vitro inhibition of the formation of fibrous aggregates of proteins (amyloids) has gained increasing attention due to the number of diseases associated with protein misfolding and fibrillation. An interesting group of compounds for which pronounced activity against this phenomenon can be expected consists of low molecular weight substances (osmolytes) which have the ability to change protein stability. Here we investigate the influence of trimethylamine N-oxide (TMAO) in acidic solution (pH=2) on the fibrillation of hen egg white lysozyme (HEWL). The process was monitored by five techniques: circular dichroism in the UV region, atomic force microscopy, dynamic light scattering, densimetry and gel electrophoresis. The obtained results show that protonated TMAO in a concentration of 400 mM inhibits amyloidogenesis. In the conditions of the experiment the HEWL molecules form clusters about 30 nm in diameter containing a relatively high fraction of covalent-bonded dimers.