It is well-known that water plays a crucial role in the folding, dynamics, and function of proteins. Here we provide further evidence showing that the aggregation kinetics of peptides also depend strongly on their hydration status, Using reverse micelles as a tool to modulate the accessible number of water molecules and infrared spectroscopy and transmission electron microscopy as means to monitor aggregate formation, we show that the rate of aggregation of two amyloid forming peptides increases significantly under conditions where limited hydration of the peptide molecule is expected to occur. These results not only are in accord with recent computer simulations indicating that the expulsion of interfacial water molecules is a key event in the dimerization/oligmerization of amyloid beta (A beta) peptides but also have implications for amyloid formation in vivo where molecular crowding is expected to influence the solvation status of proteins.