We study the mechanisms of protein aggregation and cellular toxicity by the prefibrillar oligomers formed intracellularly by amyloidogenic proteins and some of their pathological mutants. It is an accepted view that the most toxic are soluble oligomers in range of 6 to 30 mers, that are membrane seeking and even make pores into membranes (1-2). I will discuss the proposal that changed pre-amyloidogenic conformations of amyloid forming proteins may act as mutual chaperones, leading to temporary inhibition of aggregation and toxicity. Examples will be described of crystallins, prion protein and stefin B; all binders of amyloid-beta (3). Small molecule inhibitors of protein aggregation will also be discussed. Our main model protein from the family of cystatins, stefin B will be described in more detail. It’s possible function in the cell’s response to protein mis-folding will be high-lighted (4).