To become biologically active, the great majority of proteins must acquire precise three dimensional structures. This process, known as "protein folding", depends on assistance from molecular chaperones and has been recognized to be of considerable medical and biotechnological relevance. A number of human diseases are known to result, directly or indirectly, from aberrant protein folding reactions. In addition to loosing their normal function, misfolded polypeptides may form toxic species, may exert dominant negative effects, or may not reach their proper cellular location. Recently, a direct involvement of molecular chaperones in human disorders has become increasingly evident. A major area of research in my laboratory is to study proteins with similarities to molecular chaperones that, when mutated, lead to neurodegenerative disorders. Another area of my research focuses on the mechanisms underlying the inability of the bacterial cytosol to support efficient folding of eukaryotic multi-domain proteins. We have found that bacteria and eukaryotes utilize markedly different pathways for de novo protein folding, and have begun to identify the molecules and mechanisms involved in these processes.