Part One: Chaperones for genome replication and expression. Introduction: the molecular chaperone concept - R J Ellis. Neucleoplasmin and modulations of chromatin structure - R A Laskey. Microbial DNA replication - M Zylicz. The control of gene expression - S Lindquist. Part Two: Chaperones for protein folding. Protein in self-assembly - R Jaenicke. Interactions of chaperonins with folding intermediates - G H Lorimer. Chaperonin-mediated protein folding at high temperatures - M Yoshida. Chaperonin-like proteins in archaebacteria - A Horwich. Chaperones and nascent polypeptides - W J Welch. Tumour suppressor gene products as chaperones - D P Lane. Part Three: Chaperones for protein transport. Introduction - A Coleman. Microsomal protein transport - J E Rothman. Transport and assembly processes in the endoplasmic reticulum - M J Gething. Bacterial protein transport S J S Hardy. Mitochondrial protein transport - W Neupert. Part Four: Chaperones and disease. Chaperonins and the immune response - D B Young.