The determination of the X-ray structure of the actin-DNase I complex and an improved structure for plant ribulose-1,5-bisphosphate carboxylase are among the past year's advances that will aid the understanding of the role of protein-protein interactions in stabilizing macromolecular assemblies. Clear pictures of the allosteric transition have also been obtained for several allosteric enzymes. In addition, folding studies are beginning to reveal the manner in which subunit folding is coupled to subunit assembly.